Mercedes-Benz's PartsPro: Your Partner in Success

Who's Your Partner in Success?
Mercedes-Benz's f!)PartsPro
You've chosen your career as an ISP
(Independent Service Provider) because you
enjoy maintaining, diagnosing, and repairing
motor vehicles. One of the most challenging
pieces of your business is parts procurement.
Finding the right parts at the right price and
being certain they will arrive when promised
can be a challenge.
Wouldn't it be nice if there were a way to
get the parts you need w ithout the hassle
and uncertainty, so you can get back to the
important business of actually fixing cars and
taking care of your customers?
With the Mercedes-Benz PartsPro wholesale
certi Fication program, now there is!
PartsPro is a rigorous program intended
to train Mercedes-Benz dealership parts
departments on how to better take care
of you and ultimately your customers.
PartsPro certified dealers have elevated their
commitment to supporting the independent
repair channel, and will provide you with the
highest level of customer ser vice. They focus
on the things that matter most to you!
CONVENIENCE...AccuRACY...
PROFITABILITY...DELIVERY
A PartsPro dealer has the tools in place
to better meet the needs of their esteemed
wholesale customers.
For a dealership to achieve PartsPro
Certification, parts department person nel must
first undergo intensive "customer-centric"
2 Mercedes-Benz StarTuned
training which teaches person nel how to better
help YOU.
There's far more to PartsPro than just
customer-service tra ini ng. The dealership must
make specific commitments to provide "Best in
Class" service in areas such as logistics, which
includes ISP-focused parts availability, regular
delivery service, outside sales people to provide
you personalized service, as well as a dedicated
phone line and "w ill ca ll" pick up area.
THEN THERE'S TECHNICAL HELP.
On occasion we all need a helping hand. Your
PartsPro dealer is there to assist. Whether
it means providing, diagnostic assistance,
information on supplies or special tools, or
anything else you may need to assist you in
repairing your customers' Mercedes-Benz
vehicles and get them back on the road as fast
as possible.
Only those dealerships that meet the stringent
certification requirements earn the right to
display the "PartsPro" logo. Additionally, they
receive ongoing consultation and tra in ing to
ensure that they are consistently providing the
very best support to you, the ISP customer.
We hope you are already receiving indust ry
leading service from your Mercedes-Benz
dealer; however, once PartsPro Certified, we
believe you' ll be thri lled w ith the new "Best in
Class" parts-procurement experience!
Of course, you'll continue to have the
peace of mind that installing only Genuine
Mercedes-Benz parts can prov ide. I
..

TO OUR READERS:
Welcome to STARTUNED, the magazine for independent service
technicians working on Mercedes-Benz vehicles. Your Mercedes-
Benz dealer sponsors STARTUNED and provides the information
coming your way in eaoh issue.
Mercedes-Benz wants to present the information you need to know
to diagnose and repair Mercedes-Benz vehicles accurately, quickly
and the first time; text, graphics, on-line and other technical
sources combine to make this possible.
Feature articles, derived from approved company sources, focus on
being useful and interesting.
Our digest of technical information can help you solve
unanticipated problems quickly and expertly.
We want STARTUNED to be both helpful and informative,
so please let us know just what kinds offeatures and other
diagnostic services you'd like to see in it. We'll continue to bring
you selected service bulletins from Mercedes-Benz and articles
covering the different systems on these vehicles.
Send your suggestions, questions or comments to us at:
STARTUNED
One Mercedes Drive
Montvale, New Jersey 07645
Phone: 1201.263.7284
E-mail: Stefanie.A.Schweigler@mbusa.com
STARTUNED is apublication of Mercedes-Benz USA, LLC ("MBUSA"). No part of this
magazine may be reproduced without the express written permission of MBUSA.
Editorial and Circulation Offices: 1348 River Road, Montague, NJ 07827.
CAUTION: Vehicle servicing performed by untrained persons could result in serious injury to
those persons or others. Information contained in this magazine isIntended for use by trained,
professional auto repairtechnicians ONLY. This informationisprovided to inform these technicians
of conditions which may occur in some vehicles or to provide information which could assistthem
in proper servicing ofthesevehicles. Property trained technicians have the equipment, tools, safety
instru:tions, and know-how to perform repairs correctly and safety. If acondition is described, DO
NOT assume that atopic covered in these pages automatically applies toyour vehicle or that your
vehicle has that condition. STARTUNED is aregistered trademart of MBUSA.
Group Publisher
Christopher M. Ayers, Jr.
cayers@automotivedatamedia.com
Contributing Editors
Bob Chabot
bchabot@automotivedatamedia.com
Kerry Jonnson
kjonsson@automotivedatamedia.com
Michael Klaas
mklaas@automotivedatamedia.com
Tom Nash
tnash@automotivedatamedia.com
Frank Walker
fwalker@automotivedatamedia.com
Editorial Director
Bob Freudenberger
bfreud@automotivedatamedia.com
Technical Advisor
Tim Amun
MBUSA Technical Content Advisor
Donald Rotolo
Donald.Rotolo@mbusa.com
MBUSA Project Manager
Stefanie Schweigler
stefanie.a.schweigler@mbusa.com
Art Director &Circulation Mgr.
Christopher M. Ayers Ill
ayersc3@automotivedatamedia.com
Visit us at our web site
www.MBWholesaleParts.com to view this issue and past
issues ofStarTuned, along with a wealth of information on
Genuine Mercedes-Benz Parts.
To locate a Mercedes-Benz dealer near you,
go to www.mbusa.com.
IN THIS Issue
4 WHY You SHOULD Use ONLY GENUINE
MERCEDES-BENZ PARTS
There's a lot more substance to this
topic than you might think - it's not just
marketing hype. The rigorous "Genuine
Parts" testing program is especially
interesting and relevant to the price/
value relationship.
12 MODERN MOTOR MOUNTS
Mercedes-Benz has always been an
innovator in the automotive industry,
and its powertrain technology shows this
clearly. But besides the great leaps in
engines that have produced the wonderful
performance and efficiency of today,
has anybody ever given any thought to
how those engines are mounted in the
chassis? Yes, indeed, and to a larger
extent than you probably suspect.
20 MOST DEFINITELY, FROM D2B
The addition of electronics has turned
the average vehicle into a technological
marvel, but a Mercedes-Benz is no
average vehicle. At the cutting edge
of technology since its founding, the
company has added fiber optics that
allow it to process large amounts of
digital media. What do we need to know
if it stops doing that?
28 BUMPER TECH
The safety sensors are embedded in
or attached to the bumper and front
grille, which makes bumper repair
after a collision very different from the
procedures of only a decade ago.

Why You Should Use Only
Genuine Mercedes-Benz Parts
There's a
lot more
substance
to this topic
than you might
think - it's notjust
marketing hype. The
rigorous "Genuine
Parts" testing program
is especially interesting
and relevant to the
price/value relationship.
Fuel pumps need to be
j ust right, or there's
potential for noise.

In the last issue of StarTuned, we talked
about why you should use only genuine
Mercedes-Benz brake parts from your local
dealer in your service work, and we believe the
reasons we gave were pretty compelling.
We found the subject so interesting and
important that we decided to do an additional
article to explore the parts situation in
Mark Boege, a NewJersey ISP, tells StarTuned that he's
always satisfied with Genuine Mercedes-Benz parts.
general, and the rationale behind you, the ISP
(Independent Service Provider), staying with
genuine M-B O.E. components. Much of this
has to do with the company's commendable U.S.
parts-testing programs.
In the previous article, we mentioned how
genuine Mercedes-Benz brake parts were
the best things to use because they were
engineered and tailored for the characteristics
of the speci fie model involved, not just
generically one-size-fits-all. It turns out that
that's the case with most of the parts you buy
from your local M-B dealer.
OBVIOUSLY, SEEING THE ROAD CLEARLY
IS IMPORTANT TO SAFETY
Take windshield wipers, for example. With
Genuine M-B parts, their cu rve matches that of
the w indscreen of each model, so the pressure
on the blade/glass interface is optimized. Whi le
competing wiper blades are made of poured
rubber, Genuine M-B blades are extruded,
which gives better performance and a 20%lower
wear rate -- they're tested for 1.5M cycles! They
also have a helpful wear indicator that changes
When sourced from Mercedes-Benz, big assemblies, such as this 7G-TRONIC transmission ...
June 2014 5

.. or this remanufactured engine have the industry's strictest quality control, and carry unequalled
warranties. They're also often the subject of aggressive price-cutting programs.
color when replacement is needed, which
amounts to a great sales tool. Installation is far
easier and faster, too, without all the confusion
of the various attachment parts of aftermarket
versions. If you look at it over the course of
a year, this can add up to hundreds of dollars
worth of labor.
Or, how about fi lters? With cabin air filters,
the time required for installation also adds
up. Genuine Mercedes-Benz cabin filters can
be installed more quick ly because they don't
have to be modified to make them fit. Sealing
is optim ized, as well. The seal is tested for
blow-by with special equipment that measures
particles in the air.
Air filters are tested for 2,000 miles over the
same route. The tests have proved that the use
The cost of replacement engine management
computers (PCMs for Powertrain Control Modules,
to use SAE's standardized terminology) is another
thing on which Mercedes-Benz has instituted
money-saving programs.

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time. It's free, too. Just visit http:/l__epc.startekinfo.com.
of genuine air fi lters has a substantial impact
on fuel efficiency. Especial ly with diesels,
performance also goes down when a non-
genuine part is installed.
INDEPENDENT TESTING IN THE U.S.A.
We've mentioned testing, but the Mercedes-
Benz Genuine Parts Testing Program is much
more comprehensive and appropriate to our
market than you probabl y know. The testing
is designed to measure the actual impact the
quality of the part has on the customer. In
other words, for real-world situations, not for
some ivory-tower idea.
Testing is done in the U.S., which assures
that the findings are really market-appropriate.
Not only does Mercedes-Benz sell more
vehicles in this country than anywhere else,
the U.S. also has special conditions (there's
nothing in Europe equal to Death Valley),
different fuel blends, bigger
engines, and un ique regulations.
Th is is true road testing; it's not
done on a dynamometer.
The location within the U.S. is
chosen according to the type of
part being tested. For example,
testing brake pads in the brutal
stop-and-go traffic of Los Angeles
is ideal. Both genu ine O.E. and
aftermarket linings are installed
on vehicles that are cl riven on a
predefined route for one month.
The driver has a "clicker," which
he or she can hit during a braking
event that exhibits issues such
Ifyou've been in the auto service business for any length of
time, you've seen problems with the quality of aftermarket
remanufactured alternators. This is never an issue with Genuine
Mercedes-Benz parts.
as noise or vibration so that the
on-board equipment records it.
Microphones are used for brake
noise, and brake dust is measured
with a photometer. Even something
as subjective as pedal feel is
evaluated. Once again, testing is
for impact on the customer.
June 2014 7

Who conducts a this disciplined testing?
In every case, Mercedes-Benz employs
independent laboratories to be sure the resuIts
are from an objective third party and are not
skewed by brand loyalty.
CONVENIENCE, SPEED, AND ACCURACY
MBUSA offers a powerfu l tool that can
streamline your parts-sourci ng research
efforts: The EPC (Electronic Parts Catalog),
a comprehensive and easy-to-use parts look-
up system. It's a big help and time-saver in
searching for exactly the right part, assuring
that you'll always get the correct thing the
first time (which is often not the case in the
aftermarket). This will go a long way toward
avoiding the scheduling disasters that can make
customers unhappy with you. The download
is free -- visit http:/Jepc.startel<i nfo.com. We
believe you'll actually enjoy using it.
Something that's not often mentioned is the
problem you may have finding a specific part
for an older model -- Mercedes-Benz owners
typically keep their vehicles for a long, long
time, so it's likely that you'll often have cars
in you bays that almost qualify as vintage, or
even classic. You can waste a lot of time and
end up frustrated searching for parts for these
venerable vehicles from the aftermarket, whereas
the EPC covers them in detail, and inventories
are scrupulously maintained even for what are
sometimes called "heritage automobiles" (they
may very well be used as daily drivers).
There's more to electronic parts sourcing aids.
MBUSA has launched the new
www.mbwholesaleparts.com. Among its useful
features are model designation charts and
technical information resources that will help you
order the right parts and make installations easier.
Those electron ic aids combined with the
superior quality, competitive pricing, and
excellent warranty protection you get when you
make the commendable decision to purchase
genuine Mercedes-Benz parts will contribute to
your peace of mind and reputation.
PRICE/VALUE
Over the years, we've seen various carmakers
overcharge for their O.E. parts to an egregious extent,
trusting that obedient motorists or shop owners
wouldn't question the amount. One example that we
especially remember was a sensor for one upscale
make that the dealers charged over five times more
for than the same Robert Bosch part number could
be bought elsewhere.
That's not the kind of high-handed pricing
policy Mercedes-Benz fol lows. The company
does a yearly evaluation to make sure its
Genuine Mercedes-Benz replacement batteries are
made by the best European manufacturers.
Basic aftermarket catalytic converters that barely
meet EPA guidelines are notorious for having short
lives. This genuine replacement unit will last as
long as the original.

¥:cotr Workshop Resource to Get the Job Done
• WIS-net (Workshop Information • Maintenance Sheets
System}
• Wiring Diagrams
• Technical Bulletins
• Mercedes-Benz Special Tools
• Star Diagnosis System (SDS)
• Mercedes-Benz Workshop
Equipment
@ Mercedes-Benz

prices are competitive. lt's often found that
certain parts, fuel filters for instance, are
more expensive from aftermarket suppliers.
And there's never an issue with quality, fit, or
warranty protection when you go genuine.
® Mercedes-Benz
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With today's strict guidelines for antifreeze, is
there ever a reason to use anything but the exact
O.E. formula?
It can be difficult to find parts for an older
model, such as this Klima relay, from aftermarket
sources. Searching for them takes your valuable
time when you could simply go genuine and have
easy sourcing from Mercedes-Benz.
As Kerry Jonnson, one of our esteemed
technical contri butors to StarTuned, has
stated, "In the automotive repair business, our
customers rely on us to provide the type of
service that allows them worry-free operation
of their vehicles. They don't understand how
complex these vehicles have become. They
just know they need their vehicles to operate
in a safe and predictable manner. Here is
one buying decision you can make that will
help you achieve this goal." That means
"partnering" with your local Mercedes-Benz
dealer's parts department.
We'll conclude with a statement from another
Mercedes-Benz expert: "Say you have a customer
who's spent lots of money to buy a nice E-Class.
Using non-genuine parts wou ld be like replacing
a link in a chain with a paper clip. It impacts the
entire performance level of the car." I
It's not only parts, but also tools and equipment.
Where else can you get something like this
comprehensive electrical connection kit but from
your local Mercedes-Benz dealer?

It seems to be in the genes
of Mercedes-Benz engineers
to continuously look for any
possible way to improve the
company's veh icles. Every aspect
of those vehicles is thoroughly
evaluated and an incredible
amount of thought goes into
every component, both ex isting
and yet to come. Even something
as simple as a door handle is
studied and improvements are
made. Most people don't give
much thought to door handles, but
Mercedes-Benz has engineered a
stronger one so that in the event
of an accident you can get a good
grip and open the door even if
it has been damaged. This may
seem like a small improvement,
but we're sure first responders
appreciate th is simple feature.
This is how Mercedes-Benz
approaches everything that its
vehicles are composed of. Over
the years, all ki nds of dramatic
technological advancements
have been introduced into
the automotive industry, and
Mercedes-Benz has typically been
a leader in th is.
Tn recent decades, the world of
personal transportation has gone
through such rapid evolution
that perhaps "revolution" is a
more accurate word. As high
technology has taken over,
service technicians have seen
more clearly than ever before
the need to keep pace with it.
Modern electronics started with
fuel injection, ignition, and
feedback engine management
systems to control emissions
and increase fuel economy. The
electronics revolution continued
with anti-lock brake systems
(ABS), then traction control and
the Electronic Stability Program
(ESP). Mercedes-Benz was one of
the fi rst manufacturers that, in
conjunction with Robert Bosch
A.G., developed CAN (Controller
Area Networks). Th is led the
way for indiv idual computerized
systems to become integrated
and work with each other to
form systems like ESP. A ll this
computerization, of course, adds
a certain level of complexity to
our jobs when something goes
wrong. It's our responsibility as
technicians to learn continuously
so we can provide competent
diagnosis and service to our
customers. There are some
components, however, that you
probably never wouId associate
with electronic controls -- motor
mounts, for example.
PROACTIVE
There is a debate in th is country
over whether the automotive
industry has suffered more
from government bureaucracy
forcing unnecessary change, or
from the market forcing more
socially-responsible developments.
Regardless, Mercedes-Benz
has responded admirably to
these challenges. One of its
major initiatives has been the
development of diesel engines that
give luxury vehicles levels of fuel
efficiency previously achieved
only by sub-compacts, along with
astonishing performance and low
emissions. Those attributes still

wouldn't sway the American consumer, however,
if NVH (Noise, Vibration, Harshness) hadn't
been reduced al most to the levels of a gasoline
burners. One of the factors in the success of that
effort was the invention of an entirely new type
of motor mount.
Through most of automotive history, motor
mounts have been mundane. In early cars,
they were simply brackets, bolts, and nuts
that held the engine rigidly to the chassis.
Of course, that meant that all the vibrations,
jerks, and shocks that originated with internal
combustion were transferred directly to
the unfortunate driver and passengers. It
wasn't long before mitigating that motoring
unpleasantness became a priority. The first,
and longest-running, attempt at accomplishing
this reduction in vibration was the adoption
of mounts that incorporated rubber isolators
to absorb part of the unwanted harshness any
reciprocating assembly
transmits. Starting in the
early 1930s, this idea was
reasonably successfu l, if
not ideal.
Much more could be
done to isolate the delicate
occupants of a vehicle
from internal combustion's
basic brutality. So,
Mercedes-Benz engineers
developed motor mounts
that did just that.
Most of the company's
vehicles currently on
the road have hyd rauIic
engine mounts that
Engine mount design:
1. Flange 7. Hub
2. Seal bellows 8. Retaining ring
3. Diaphragm 9. Cover
4. Check ball 10. Bore
5. Buffer stop 11. Solenoid
6. Protective cap
go beyond the simple
idea of using rubber's
compressibility to reduce
roughness -- oiI is the
medium used to dampen
the vibration a running
The two-wire harness is a surefire give-away that this is a computer-
controlled mount. It is powered up by fuse F58. Ifyou unplug the fuse
and plug it back in with the key on, you should hear the mounts click.

---- ;-_:: ... - ~·
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With a paid subscription to www.startekinfo.com you can access wiring diagrams. Here, you can see that
components Y123 and Y123/1 are the switchable engine mounts. They're wired together so both mounts
get grounded at the same time by the ME.
Ml (Fuel pump)
M4n (Combustion engine and air
conditioning with Integrated control
fan motor)
M16/6 (Throttle valve actuator)
M55 (Intake port shutoff actuator
a motor)
Ulll R39/1 (Vent line heating element)
• R4B (Coolant thermostat heating
l!!!I element
•!--II Y77/1 (Boost pressure posttloner)
YB5 (Exhaust gas recirculation
cooler bypass SWltchover valve)
Y2719 (Exhaust gas recirculation
actuator)
Diagnostic glowing
Injector shuto!T
Status of associated actual value
Name Actual value Spacllledl4••
Switchable engine mounts Fault. 53336/6058
I:> Actuate components ·y123 (Len switchable engine mount)' and 'Y123/1 (Right switchable engine
mount)'.
Terminate actuation.
Ifyou have made the investment in Xentry, you have the ability to bi-directionally control outputs. One of
these is the switchable engine mounts.
June 2014 15

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engine generates.
Somewhat similar
to the principle 0 ... . - . ~ c:> o:o: t...- ·]a lil f- ·,;..,:Jc.:i - · - · ,.,.,.,
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of a suspension
shock absorber,
the oi I is forced
through an orifice
between two
chambers at the
top and bottom of
the mount as they
are compressed
and expanded
;11~R!ii!iliim!!i=iliiiil...
[
by engine shake.
When these fail,
it's from a loss
of fluid, and
typically causes
a more sudden
These modern motor mounts are still serviced in the same way as a conventional
unit with the minor exception that there is an electrical connector to unplug. With
your paid subscription to www.startekinfo.com, you can access WIS and get a
step-by-step procedure for diagnosing and replacing the new mounts.
and pronounced
clunking than you'd get from a gradually-
dissolving rubber mount. Diagnosis is mostly
a matter of observation. ls the bottom chamber
flat? Is there oil present?
Speaking of the working fluid, whenever
you're trying to track down an oil leak, say
from a cam or timing chain cover, don't
overlook the possibility that the real culprit is a
ruptured motor mount. We should also mention
that some aftermarket parts suppliers substitute
ordinary rubber mounts for the hydrau lic type,
wh ich is another reason you should stick with
Genuine Mercedes-Benz parts.
COMPUTER CONTROL?
While hydraulic motor mounts work quite
well, they're still passive. They have no ability
to adapt to the differi ng cond itions encountered
as engine modes change. Since transforming
the public perception of the characteristics
of diesel-powered cars is turning out to be a
lengthy process, Mercedes-Benz has been doing
everyth ing possible to reach that goal. Not
only with sophisticated common-rail injection
with multiple events and ingenious after-
treatment of the exhaust, but also by givi ng
an unsung and overlooked part a fresh look:
the lowly motor mount. In order to endow its
diesels with a smoothness that rivals that of a
gasoline engine, Mercedes-Benz has developed
computer-controlled mounts.
These new "electric" or "switchable" engine
mounts were introduced in 2011 on the
Mercedes-Benz M-Class with the 642 diesel
(166 Chassis). Instead of hyd raulic oil, they
use air contained in three bellows. An internal
electrical solenoid valve either connects the
air chambers together, offering a large volume
of air for the compression and expansion that
absorbs vibrations, or closes off the chambers
from one another for a firmer mounting (the
default position is the "hard" setti ng with the
chambers isolated).
Two wires run from the harness to the
solenoid, one 12V, and the other ground, which
is controlled by the ME (Motor Electronics).
Even with sophisticated common-rail injection,
diesels can be rough during cranking and

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Here we are looking at the activation of the switchable engine mounts with the Xentry software. Notice
how the ME simply grounds the solenoids in the upper trace. The lower trace shows the amperage draw
of a single engine mount.
starting, and tend to shudder when shut
down. So, the ME is programmed to activate
the solenoid during these modes, making a
relatively-large volume of air available to absorb
any harshness. This is ca lled the "soft" setting.
The solenoid is either energized or off, there's
no in-between.
XENTRY AND DMM
Although you may not be seeing these mounts
for years, you shou Id sti11 know how to diagnose
them. If you've invested in Xentry software, you
can activate the solenoid at w ill and monitor
both the amp draw and the computer's ability
to control the ground side of the circu it. You
can also use your DMM (Digital Multi-Meter)
to check the resistance of the solenoid and look
for an open windi ng. You should read about 27
ohms with a good solenoid.
The power feed is fuse F58. This fuse also
supplies the diesel fuel injection system
solenoids, the pressure regulating valve, and
the quantity control valve. So, a short circuit
or any other fai lure that causes the fuse to blow
wi ll cause a no-start cond ition, and the mounts
wi ll default to "hard," which won't be noticed
with the engine stopped. These mounts may be
incorporated into other models in the future, so
be sure to check the w iring diagrams for the
car at hand by visiting StarTek lnfo.com.
Removal and replacement is basically the
same as with any other engine mount. There
are two fasteners that hold it to the engine
sub-frame, and a single fastener to the engine
mounting bracket. The only additional step is
unplugging the electrica l connector.
As we said earlier, with modern technology
being applied to more and more aspects of
automobiles, it is your responsibility as an
ISP (Independent Ser vice Provider) to keep
pace with these changes and continue your
education. This allows you to keep giving your
customers what they expect from you. It's also
in your own best financial interests. I
June 2014 17

er ormance.
uccess.With our competitively priced Genuine Remanufactured Parts, you no longer have to settle for anything
less than Mercedes-Benz quality. But that's just part of the story. You see, our airmatic struts,
catalytic convertors, turbochargers and steering racks all carry a 12-month, no mileage-restriction
warranty. So our parts are not only a great deal. They're agreat value. And since they're genuine
Mercedes-Benz, you can have confidence they'll last, and so will your relationship with your customers.
Contact an authorized Mercedes-Benz dealer or learn more at www.mbwholesaleparts.com
.
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A 000 230 7011 80
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ft One remanufactured engine pulls the plug on climate-damaging
~I C02 and saves 447 days of power for one laptop.
A 163 '490 971'4 80
@-
•MSRP excludes state and local taxes and freight if applicable. Price excludes core deposit. Price valid as of February 2014. Prices may vary by dealer.
See your authorized Mercedcs·Benz dealer for additional details or a copy of the Mercedes-Benz parts limited warranty.

A 164 460 0300 80
Mercedes-Benz

MOST Definitely, from D2B
The addition ofelectronics has turned the
average vehicle into a technological marvel, but
a Mercedes-Benz is no average vehicle. At the
cutting edge oftechnology since its founding, the
company has added fiber optics that allow it to
process large amounts ofdigital media. What do
we need to know ifit stops doing that?
One of the first steps in diagnosing a problem with the MOST bus system is to establish communication
with the MOST master control unit. In this case, it is the COMAND®radio. Verify communication first.
If you do not have communications, check the fuses, power, and ground to the control unit. If you have
communication, you can move on to the next step.

We've all seen electronics take hold of our
industry. It started with electronic ignition
(mandated in 1975), then fuel injection, and now
seemingly every component on the car is either
controlled or monitored by electronics. This
generally makes systems more complicated. There
are sensor inputs, a processor, and computer-
controlled outputs. While this added complexity
can make your life more difficult when something
breaks, it can also make it easier.
SDS XENTRY software is designed to interpret
the data of the processors and can retrieve
diagnostic trouble codes, give you real-time data,
and also allow you to bi-directionally control
computer outputs so you can find out if the
components receiving commands are actually
working. Having this in formation allows you
to quickly look at data you may find useful in
diagnosing the problem. Once you isolate where
the trouble is, you can then do more specific
electrical testing to verify your conclusions.
You'd feel pretty silly if you spent hours doing
high-tech diagnosis only to find out that an
electrical connector was not plugged in properly.
GETTING THE MOST
Nowhere is this technology more evident
than in the entertainment system. These have
different needs from body control or powertrain
systems. Powertrain systems need high-speed
data transfer because traction control, engine
management, and suspension features need
to work together to keep the car under control
during spirited drivi ng. Body control systems
ca n operate at a much slower speed and the
vehicle's occupants won't notice the difference.
Entertainment systems do not need high speed,
but there is a whole lot of in formation that needs
to be moved around --visual and audio media
files are large. This in formation must be sent
from the digital media reader (CD/ DVD player),
the display screen, and the sound system. If
these systems transferred information across
electrica l lines the w iring involved would have
to be very complex. For this and other reasons,
Mercedes-Benz has chosen to use fiber optics for
transferring digital media.
Fiber-optic systems offer many advantages
over conventional electrica l wiring. Number
With a paid subscription to www.startekinfo.com, you can pull up a chassis-specific wiring diagram.
You can compare the wiring to the MOST bus list of control modules and locate each component.
Notice that the Orange lines are wired in series. This is the fiber-optic line. The purple wire is the
electrical "Star" wiring electrical bus the MOST master uses to see which control units are waking
up and which are not.

one, they are capable of carrying large amounts
of data very quickly. Number two, fiber-optic
systems send Iight messages along a cable, so
they're not subject to magnetic interference, or
RF!. They do require a discrete fiber-optic line
routed with the wiring harness, which does acid
a level of complexity. Fiber-optic cable is fairly
sturdy, however, and is not subject to corrosion
from water intrusion as electrical wiring is.
The main rule for routing fiber-optic cable
is simply not to bend it enough to crimp it.
Usually, you don't have to worry about the cable
unless accident damage has compromised it. In
that event, replace it.
MASTER
Mercedes-Benz started its adoption of fiber-
optics with the D2B (Domestic Digital Bus)
system, which was developed exclusively by the
company. The network is routed in series -- there
is one fiber-optic cable coming in and another
coming out. In order for this system to work,
"someone" has to be in charge, so every D2B
system has a "master." This is the one control
unit that is in charge of all the others. Th is is
important to know because th is is the control
unit you are talking to when you communicate
with it using the XENTRY diagnostic software.
Since the fiber-optic network is routed in
series, it is important for the coding of the
master control un it to not only k now all of the
components on the fiber-optic ring, but also the
order in which they are connected. Not every
D2B system is the same --someone may have
ordered a car with or without a multiple-disc CD
changer, for example.
Another thing that's important to know about
a series-wound fiber-optic system is that if one
component fails it can bring down the whole
system. Nothing will work. You may th ink it
would be a big undertaking to diagnose a whole
system that is not working, but it is really
not that di fficuIt. The First th ing you need to
establish is communication with the master
Locate the first component on the fiber-optic bus
and unplug the connection to that unit. When you
turn on the ignition key, you should see one of
the cables light up with the fiber-optic signal as
shown here. Plug it back in and move on to the
next control unit untily ou no longer see the cable
light up. This means either the cable is bad, or the
control unit before it is not putting out a fiber-
optic signal.

control unit. In the case of the D2B system,
the master is the COMAND® control unit -- the
interface mounted in the center of the dash. Use
your XENTRY software, or equiva lent, to try to
establish communication w ith the master. If you
do have communication, then you can assess
live data about the other control units on the
028, pu11diagnostic trouble codes that may lead
you to the problem, or "ping" the control units
on the D2B bus and see what answers back.
STARTING POINT
If you do not have commun ication w ith the
master COMAND® un it, that's the first thing
you must fix. Start with check ing power,
ground, and the wake-up signal to the control
unit. Remember, if the master is not functioning
then nothing else will, either. The first thing
you should check are the fuses that power
up the master COMAND® unit. If the fuses
have power, the next step would be to pull the
COMAND® unit out and veri fy the power and
ground supply to it -- check for damaged or
corroded wiring. lf you have power and ground,
then you may want to put a lab scope on the
CA lines to the COMAND® unit and verify
that the scan tool communication signal is
making it to the module. If everything is there,
then you may simply have a bad COMAND®
unit. Mercedes-Benz offers remanu factu red
units through you r Mercedes-Benz dealer's
pa rts department.
If you have commun ication with the
COMA ND® unit, then the diagnosis is even
easier. If the system is down, it has probably
set a diagnostic trouble code in the COMAND®
unit. This will probably lead you to the trouble,
but even if it doesn't there is testing you can
perform to isolate the problem. From the master
COMAND® unit, you ca n cal l up the coding for
the unit and you w ill k now what options are
installed in the vehicle you are work ing on.
This is a big help in diagnosing the fiber-optic
system. What you ca n do at this point is access
the first control unit the fiber-optic signal is
sent to and unplug the cable from that control
unit. Turn the ignition l<ey on and observe the
Ifyou purchase a fiber-optic loop, you can bypass a possibly bad control unit. If the system starts to work,
you'll know the control unit is the problem. Before replacing the control unit, verify that it has the proper
power supply feed, ground, and wake-up signal.
June 2014 23

cable plug. You should see one of the cables
blinking. This is the optical wake-up signal
from the master.
THE NEXT STEP
If you see the blinking light, you know the
master is putting out the optical wake-up
signal. You can then plug the connector back
in and move on to the next control unit on the
fiber-optic bus. Unplug that connector, turn
the ignition key back on, and watch for the
same bl inks. Keep moving on through the next
control units until you no longer observe the
blinking. Remember, the Fiber-optic network
is in series. So, the control unit that you just
unplugged is not the one you're testing. You're
looking for the output signal from the control
unit before it's on the bus. If you no longer see
the wake-up call, it is either not coming out of
the control unit before it's in the network, or the
cable has a break in it.
You can purchase a special fiber-optic loop
tool, which is sort of
like a jumper wire. You
can plug it into the
fiber-optic connector
of each control unit
the fiber-optic network with an electrical
wake-up line. This signal is generated by the
master control unit, but it is conventionally
wired in parallel. The wake-up signal is sent
and each control unit answers on this wake-
up line. The control unit that does not respond
has failed. This is how the master control unit
senses the system failure and sets diagnostic
trouble codes. Veri fy power and ground and
you have diagnosed the problem.
EVOLUTION, NOT REVOLUTION
The only real difference between the D2B
bus and the next evolutionary stage, the
MOST (Media Oriented System Transport), is
the communication protocol. The diagnosis is
exactly the same. Use XENTRY to compare the
electrical wake-up signal and compare it to
the fiber-optic network. The two special tools
for the D2B and MOST system are inexpensive
and available from your local Mercedes-Benz
dealer's part department -- remember, they're
happy to help. I
on the network. If you
turn the key on and the
system starts to work,
then the control unit
you just bypassed is
. Transport Screvv Rernova l Advice
the problem. This does
not mean the control
unit is necessaril y bad.
You sti 11 need to verify
power, grounds, and the
wake-up signal at that
control unit, starting
with the fuses that
power it up.
Mercedes-Benz has
made diagnosis even
easier by backing up
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The MOST bus is programmable with XENTRY software. Remember, ifyou
want to add a component to the MOST bus you need to go into the MOST
master and change the coding for the new configuration. You must get the
order right in the fiber-optic loop for stable MOST bus operation.

Mercedes-Benz Mobil 1
Product Name Part Number Quantity Product Description Recommended Consumer Applications
MercedeirBenz SPEC.
BQ 1090144 Bulk - No Equipment
Mobil 1 BQ 1090162 6/1 Quart Cases
Fully synthetic formulas designed Low SPAsh. Available at most MB dealers
Formula M 5W-40 specifically for gasoline passenger cars
BQ 1090151 55 Gallon Drum
Genuine A0009898301USB6 12x1 Quart Cases ·
Mercedes-Benz Oil Fully Synthetic formula specifically . .
MB 229.5 A0009898301USBB 55 Gallon Drum designed for Mercedes-Benz engines Mercedes-B.e.nz Engines that require
Specification that require the 229.5 Specification 229·5 Specification Oil
SAE 5W-40 A0009898301 USB9 Bulk - No Equipment
BQ 1090010 Bulk - No Equipment
Fully synthetic formulation designed
Porsche A40. Many European vehicles.
Mobil 1 OW-40 BQ 1 09 0015 6/1 Quart Cases to meet the requirements of many
European vehicles
HT/TS applications.
Mobil 1 ESP BQ 1090135 Bulk - No Equipment
Formula M 5W-40 Advanced full synthetic formulas
designed specifically for diesel Low SPAsh. Available at most MB dealers
BO 1 09 0142 6/1 Quart Cases passenger cars that have particulate
BQ 1 09 0143 55 Gallon Drum
filters
Higher viscosity, advanced full synthetic
BQ 109 0134 6/1 Quart Cases
formula designed for performance Porsche A40. HT/HS applications.
vehicles
Extra high performance automatic
Recommended tor use in Mercedes-Benz
BO 1 09 0166 55 Gallon Drum transmission fluid formulated with
selected HVI base oils
automatic gearboxes
Advanced full synthetic formulas Low SPAsh. Available at most
BQ 109 0165 12x1 Liter Cases designed specifically for passenger car
MB dealers.
diesels that have particulate filters
1
AdBlue• 1/2 Gal. A 000 583 0107 1/2 Gallon Bottle Non-toxic solution that transforms
Recommended for use in Mercedes-
harmful Nitrogen Oxide (NOx) emissions
Diesel Exhaust Fluid
BQ 1470002 55 Gallon Drum from diesel-powered vehicles into
Benz, Volkswagen + BMW AdBlue• (DEF)
55 Gal harmless water vapor and nitrogen
applications
BQ 1090017 6/1 Quart Cases Advanced full synthetic formulation
designed to meet the requirements Vehicles that require 5W-30. Corvette
BQ 1090018 55 Gallon Drum of many domestic, including GM, and approved.
im orted vehicles
BQ 1 09 0019 6/1 Quart Cases
Mobil 1 lOW-30 BQ 1090020 16 Gallon Keg
Advanced full synthetic formula
designed for domestics and imports
Vehicles that require 5W-30 or lOW-30
BQ 1090083 6/1 Quart Cases
vance u synt et1c ormu at1on
Mobil 1 5W-20
designed to meet the requirements of
Vehicles that require 5W-20
BQ 1090084 55 Gallon Drum many newer vehicles including Hondas,
Eords Cbr>!slers aad aewer Iaimtas
BO 109 0169 6/1 Quart Cases Advanced full synthetic formulation Most vehicles that specify OW-20 (newer
Mobil 1OW-20 AFE designed for enhanced fuel economy Toyotas and Hondas), 5W-20 and certain
BQ 109 0168 55 Gallon Drum and cold weather performance hybrids
Mobil 1 OW-30 AFE BQ 1090174 6I1 Quart Cases
Advanced full synthetic formulation
Most vehicles that specify 5W-30 ordesigned for enhanced fuel economy
and cold weather performance
lOW-30
BQ 1090164 6/1 Quart Cases Multi-vehicle, fully synthetic fluid
Vehicles that require Dexron Ill, Ford
Mobil 1 Synthetic ATF
designed to meet the demanding
BQ 1090163 requirements of modern passenger Mercon and Mercon V performance
55 Gallon Drum
vehicles levels
Mobil 1 15W-50 BQ 1090023 55 Gallon Drum
Boosted, higher viscosity, advanced
HT/HS applications. Racing and Flatfull synthetic formula designed for
performance vehicles
tappet applications
Mobil 1Gear Oil Exceeds the most severe service
SUITABLE for use in modern high
(Mobil 1 Gear Lube BO 1 09 0085 12/1 Quart Cases requirements in both conventional and
performance automobiles like SUV's,
75W-90) limited slip applications Vans and Light duty trucks requiring API
GL-5 level performance

M ercedes-Benz automobiles are designed to perform on
the most challenging roads and conditions. Shouldn't the oil
used in Mercedes-Benz engines do the same? We think so.
That's why Mercedes-Benz and Mobil 1 have partnered to
offer an unbeatable combination of total engine performance
and driving luxury.
Please have a look at our oil portfolio which is available
through your local Mercedes-Benz dealer. Our dealers are able
to offer you a wide variety of oil grades at competitive prices.
Product Name Part Number Quantit Product Descri tlon
Mercedes·Benz SPEC.
Mobil 1 Gear Oil Exceeds the most severe service
(Mobil 1 Gear Lube BO 109 0085 12/1 Quart Cases requirements in both conventional and
75W-90) limited slip applications
BO 1 09 002464 Bulk - No Equipment Formulated from quality base stocks
BO 1090171 12/1 Quart Cases
combined with modern performance
Mobil Special 5W-30 additives to give the engine the expected
BO 1 09 003064 55 Gallon Drum
protection and performance under a
wide variety of operating conditions
BO l 09 003164 Bulk - No Equipment Formulated from quality base stocks
Mobil Special lOW-30 additives to give the engine the expected
BO 1 09 003764 55 Gallon Drum
Mobil Special lOW-40 additives to give the engine the expected
BO 109 004464 55 Gallon Drum
Mobil Special 5W-20 additives to give the engine the expected
BO 109 013264 55 Gallon Drum
Formulated from quality base stocks
Mobil Special 20W-50 BO 1 09 004664 55 Gallon Drum additives to give the engine the expected
BO 1090053 Bulk - No Equipment Extra high performance diesel engine
BO 1 09 0058 12/1 Quart Cases
oils that help extend engine life in
Mobil Oelvac 1300 the most severe on and off-highway
Super 15W40 BO l 09 0059 4/ l Gallon Cases
applications while delivering outstanding
performance in modern, high-output,
BO 1090060 55 Gallon Drum low-emission engines including those
with Exhaust Gas Recirculation (EGR)
Mobil Delvac 1300
and Aftertreatment Systems with Diesel
Super 10W30
BO 1090086 Bulk - No Equipment Particulate Filters (DPFs) and Diesel
Oxidation Catalysts (OOCs)
BO 1 09 0051 4/ 1 Gallon Cases Fully synthetic supreme performance
heavy duty diesel engine oil that helps
Mobil Delvac l 5W40
extend engine life while providing long
BO 1090052 55 Gallon Orum drain capability and fuel economy for
modern diesel engines operating in
severe applications
BO 1 09 0078 60/14 oz Cartridge
BO 1090079 120 lb Keg
Formulated to provide excellent high
Mobil Grease temperature performance with superb
XHP 222 BO 1090080 400 lb Drum adhesion, structural stability and
resistance to water contamination
BO 1090098 40/14 oz Cartridge
BO 1090096 120 lb Keg Extra high performance. automotive
Mobil Lube HD lubricant formulated from select base
Plus BOW90 BO 1 09 0097 400 lb Orum oils and an advanced additive system
specifically for limited-slip differentials
Recommended Consumer Applications
SUITABLE for use in modern high
performance automobiles like SUV's,
Vans and light duty trucks requiring API
GL-5 level performance
Recommended for gasoline fueled
automobiles and light duty trucks
requiring an API SN/SM/SL/SJ
automobiles and light duty trucks where
a higher viscosity API SN/SMSL/SJ oil is
preferred or recommended
automobiles and light duty trucks where
a higher viscosity API SN/SMSL/SJ oil is
preferred or recommended
Specifically recommended for the
latest low-emissions, high performance
diesel applications equipped with
aftertreatment systems using Diesel
Particulate Filter (DPF) and Diesel
Oxidation Catalyst (DOC) technologies
Recommended for use in all super high
performance diesel applications, including
modern low emission engine designs with
Exhaust Gas Recirculation (EGR)
Recommended for industrial and marine
applications, chassis components and
farm equipment
Recommended for use in limited-slip
differentials, axles, and final drives
requiring APl GL-5 level performance

Bumper Tech
Mercedes-Benz Safety Systems Help Avoid
Accidents and Significantly Change Bumper Repair
Mercedes-Benz safety technologyfeatures state-ofthe-art sensors
that constantly monitor the position ofthe vehicle relative to
other vehicles and obstacles. Software analyzes sensor data and,
ifnecessary, sends commands to various safety systems to alert
the driver to a potential problem. If the driver does not respond
quickly, the system can pre-pressurize the brake master cylinder,
reduce speed, or stop the vehicle, apply the brakes in a manner
that prevents an unsafe lane change, or backing into an already-
occupied space, and adjust seat belts, seat position, head rests,
and other supplemental restraint components in preparation for a
possible collision. All ofthis is made possible by short- and long-
range radar and other sensor technologies. The safety sensors are
embedded in or attached to the bumper and front grille, which
makes bumper repair after a collision very different from the
procedures ofonly a decade ago.
There are six Parktronic sensors in the front bumper of this 2010 GL 450. The small round sensor heads
blend beautifully into the bumper, and enable several different safety functions, including adaptive cruise
control, lane departure warning, and other collision avoidance systems.

Mercedes-Benz safety technology features
state-of-the-art sensors that constantl y monitor
the position of the vehicle relative to other
vehicles and obstacles. Software analyzes
sensor data and, if necessary, sends commands
to various safety systems to alert the driver
to a potential problem. If the driver does not
respond quick ly, the system can pre-pressu ri ze
the brake master cylinder, reduce speed, or
stop the vehicle, apply the brakes in a man ner
that prevents an unsafe lane change, or
backing into an already-occupied space, and
adjust seat belts, seat position, head rests,
and other supplemental restraint components
in preparation for a possible collision. A ll of
this is made possible by short- and long-range
radar and other sensor technologies. The safety
sensors are embedded in or attached to the
bumper and front grille, which makes bumper
repair after a collision very different from the
procedures of only a decade ago.
Automotive safety strategies have historica lly
been passive in nature. Seatbelts, ai rbags,
bumpers, and other devices sought simpl y to
reduce the impact of a collision on the vehicle
and its passengers. Over the past 15 years or
so, however, new safety technologies have been
developed that emphasize accident avoidance,
and in more active ways than could be imagined
only a few decades ago. Much of th is new safety
technology features high-tech sensors that
see th rough the Mercedes-Benz front and rear
bumpers, so bumper repair is no longer a simple
straighten, patch, and re-paint job.
For example, ordinary cruise control keeps
driving speed at a pre-set pace, but Adaptive
Cruise Control helps maintain the desired
distance between the vehicle and the one
immediately ahead. This function is enabled by
the Mercedes-Benz Distronic Plus system.
Distronic Plus features a combi nation of
short-range radar sensors beh ind the bumper
cover and a long-range sensor in the front
griIle. These sensors together measure the
distance between vehicles, and allow the
electronic logic to determine whether or not
that gap is decreasing. The software assesses
how quickly the gap is decreasing and
determines how much braking power is needed
to restore the gap to the preferred length. The
system then progressively applies the brakes
to slow the vehicle and restore the gap to the
desired distance.
There are four Parktronic sensors in the rear bumper of this 2010 GL 450. Parktronic sensors in the rear
help with lane departure warning and Parking Assist functions. There are similar sensors in the front
bumper on many Mercedes-Benz models.

A vehicle traveling at 50 k mh (31 mph)
covers 20 m (65 ft.) in two seconds. Adaptive
Cru ise Control alerts the driver to a dangerous
situation via flashing lights in the dash or Head-
Up Display, but does not wait for him or her to
take action. Mercedes-Benz Distronic Plus radar
technology is never vu lnerable to the things
that sometimes distract humans from the road
ahead, and it responds faster and w ith more
precise application of braking force than any
driver could, no matter how skilled.
Mercedes-Benz Pre-Safe Brake is another
example of active safety strategy. Pre-Safe
Brake sensors scan the road ahead for potential
problems. If they detect a vehicle ahead
slowing, stopped, or crossing its path, or "see"
pedestrians or other obstacle, the system alerts
the driver.
Pre-Safe Brake simultaneously initiates up
to 40%of the available braking power. When
the driver brakes, the appropriate amount of
braking pressure is instantly applied, all the
way up to 100% if the driver so chooses. And
should the driver fail to respond, the system
will apply full braking on its own, to help
avoid or reduce the intensity of a collision.
Independent studies show that this pre-
charging of the brakes shaves enough off of the
driver's reaction ti me to effectively increase
the occupant survival rate in an accident by 10
to 15%.
This ability to take control of vehicle brak ing
is only part of the Mercedes-Benz active safety
strategy. Pre-Safe also adjusts vehicle restraint
systems withi n milliseconds, to prepare for
a potential accident. Tt tightens the front seat
belts, adjusts the front head restrai nts and
passenger seat, and, if the vehicle is equ ipped
with the Mercedes-Benz Memory System, can
even close the windows and sun roof.
HIGH-TECH BUMPER CARE
Suppose a customer comes in with the
complaint that after a minor front collision, the
Adaptive Cruise Control no longer works. You'll
need to add to your traditional coll ision-repair
knowledge in order to help this motorist.
Mounted in the front bumper cover on
vehicles eq uipped with the Parktronic system
are six ultrasonic sensors. They can not
Collision avoidance sensors sit behind plastic grille covers in each side of the front bumper of this 2014 ML 350.

>
be repaired. If one has been impacted in a
collision, it must be replaced. Even if only a few
scratches penetrate the paint and dig into the
sensor surface, complete replacement of the
sensor is required.
If the repair involved replacement of the
Distronic (DTR) control un it, the sensors that
monitor rotationa l speed, yaw rate, and lateral
acceleration, or of the steering column tube
module, the DTR control unit must be initialized
and recalibrated.
Another possible cause of problems with
the short-range radar sensors is the sealing
ring where the sensor seats into the bumper.
The sensors and con nectors are designed to
be waterproof, and to resist a high degree
of vibration and shock. If the sealing ring is
damaged, it may allow vibration or moisture to
overwhelm the sensor. A damaged seali ng ring
should be replaced.
PAINTING BUMPERS
Have you had a customer bring in a vehicle
with the complaint that after another shop
repaired a bumper, the backup assist,
lane departure warning, or other collision
avoidance system no longer works? It could be
the paint job.
When painting the bumpers, it is important
to ensure that the paint coat on the short-range
radar sensors is of only minimal thickness.
Too thick a coat can lead to malfunctions
because the sensors see it as an obstacle in the
vehicle's path, rather than as merely excessive
paint thickness. The system will respond by
either keeping the warning lights or beepers
constantly on, or shutting down completely after
a certain amount of time to prevent full-time
appl ication of the brakes and activation of key
elements of the supplemental restraint system.
The maximum paint thickness allowed at
the sensors is the primer and two coats of
paint (color and clear). Primer, color, and clear
together count as one refinish, but the painter
MUST be mind fu I of keeping each coat as
minimal as possible.
We shou Id mention that pre-painted sensors
are available for certain popular colors.
When it detects an obstacle (like the two-by-four stud we placed in front of this vehicle), the Parktronic
system begins flashing red lights in two places on the dashboard.
June 2014 31

The scuffing over the Parktronic sensor in the rear bumper of this 2010 GL 450 is enough to require sensor replacement.
PLASTIC: REPAIR OR REPLACE?
Damage to bumper covers and protective
bumper strips in the form of cracks, holes, and
scuff marks deeper than one millimeter can be
fi xed using the Teroson plastics repair k it (see
the approved materials Iist at
http://portal.aftersales.i.daim!er.com in the
paint technology guidelines section).
The Teroson kit includes a cleaner that
removes dirt, grease, and other contam inants, a
primer that prepares the surface for fi ller, a two-
part adhesive filler, and a glass fiber mesh. The
filler hardens in 15 minutes under an infrared
lamp. The fiber mesh rei nforces the adhesive to
help resist repair failure due to expansion and
contraction of the plastic over ti me.
With six sensors in the front and four in the
rear bumper, it is easy for filler that is feathered
out from the damaged spot to overlap one or
more sensors. The addition of primer, basecoat,
and clearcoat can then quickly build up to
levels in excess of paint thickness maximums,
renderi ng the affected sensors inoperable. If the
damaged area is close enough so that the fi ller
would overlap the sensor, replace rather than
repair the bumper.
Mercedes-Benz short-range ultrasonic Parktronic
sensors insert directly into the back of the plastic
bumper, and include a seal that helps them resist
road-induced vibration and shock.

BUMPER BASICS
A MJrcedes-Benz bumper consists of three
or four basic components: a decorative plastic
bumper cover, a foam impact absorber bar, a steel
or aluminum reinforcement bar, and, depending
on the vehicle model, outer protective strips.
The foam impact absorber bar is located
between the decorative cover and the metal
reinforcement. Its purpose is to compress and
absorb some of the damage in a low-impact
col lision. Be careful when handling the foam
inserts, as they snap easily.
The metal reinforcement bar attaches to the
front crossmember and is designed to absorb
some of the energy of a low-impact collision.
In a two or three mile per hour "parking lot"
incident, the damage to the vehicle may be
limited to the bumper cover, impact absorber, and
reinforcement bar.
The Mercedes-Benz reinforcement bar
is a si ngle-use component, and cannot be
repaired. If it has been damaged, it must
be replaced.
Some models feature outer protective
strips. A lthough primarily decorative,
t hey are sacrificial plastic pieces. They are
inexpensive and snap on using clips, so
they are easil y replaceable i n the event of
mi nor impact or scratch damage.
BOLT-ON MODULES
Front and rear modu Jes absorb and deflect
some of the impact energy of a col Iision
away from valuable mechan ical components.
The modules bolt on to the upper and lower
longitudinal members (frame rai ls). The
bolt-on design helps reduce repair ti me and
cost ver sus a welded fu 11 frame.
An aluminum reinforcement bar is built onto the crossmember of the front module. A foam impact
absorber sits between the decorative bumper cover and the reinforcement bar.
June 2014 33

ADDITIONAL CONNECTORS IN
MERCEDES-BENZ FRONT BUMPERS
• Washer Fluid Reservoir - On vehicles
with a Headlamp Washer System, you
must detach the electrical and fluid
hose connections from the windshield
washer fluid level indicator switch and
pump, and remove the Washer Fluid
Reservoir in order to access and replace
the front bumper.
• The Outside Temperature Sensor - clips to
the front bumper, and must be disconnected
in order to remove the bumper.
THE FEW, THE PROUD, THE
KNOWLEDGEABLE
These new safety features are based on
cutting-edge sensor technology and are now
being seen for the first time by many coll ision
repair technicians. Dig into your Mercedes-Benz
train ing information and learn how the systems
work. You'll find that knowing where a sensor
is located, how it must be positioned to "see" so
it can accurately esti mate the vehicle's position
relative to nearby objects, and how your repair
prep and painting procedures must adjust to
avoid interference with sensor operation will
make you an in-demand expert in your market. I
The Mercedes-Benz front module bolts onto the upper and lower frame rails. In a low impact (up to eight
mph) accident, the front module may absorb all of the collision energy as it crumples, leaving the frame
rails undamaged. In that scenario, repair involves simply bolting on a new front module.

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