2. TO OUR READERS IN THIS ISSUE
We lcome to StarTuned, th e
magazine for independent service
4 ANOTHER CHANCETO BURN
tech nicians working on Mercedes- Just like a blacksmith's bellows, the Mercedes-Benz AIS
Be nz veh icles. You r Me rcedes- Benz "fans the flames," promoting rapid oxidat io n of pollutants
dea ler sponsors StarTuned and in the exhaust stream.
provides the information coming
your way in each issue .
Mercedes-Benz wants to prese nt the
inform ation you need to know to
10 SAFE & SECURE -
diagnose and repa ir Mercedes-Benz MERCEDES-BENZ PNEUMATIC
cars accurate ly, qu ickly and the f irst CENTRAL LOCKING
t ime ; text, graph ics, on-l ine and other One of the convenience features used most by your
techn ica l sources comb ine to make
customers is the central locking system. Years ago,
this possib le.
M-B took a completely different approac h to t his by
Feature articles, derive d from
making it pneumatic instead of electrical.
approve d company sources , focus
on bein g useful and interesti ng.
Our digest of technica l information
can help you so lve unant icipated 16 A QUESTION OF TIMING
prob lems qu ickly and expertly. Mercedes- Benz timing chains and tensioners last
Our list of Me rce des-Benz dealers
and last. But, given the tremendous numbe r of
can help you f ind Genuine
miles people put on these vehicles, they will need
Merced es-Benz Parts.
attention sooner or later.
We wa nt StarTuned to be both
he lpfu l and informative, so please let
us know just what kinds of features
and other diagnostic services you'd 26 THE STRAIGHT & NARROW
like to see in it. We'l l continue to When evaluating chassis integrity after collis ion damage
bring you selected service bu ll etins you need to take the extra steps to verify st raightness.
from Me rcedes-Benz and artic les The inherent value of a Mercedes-Benz veh icle definitely
covering the different systems on makes these extra steps worthwhile.
these vehicles.
Send your suggestions, questions
or comments to us at:
StarTuned
31 GENUINE MERCEDES-BENZ
One Mercedes Drive PARTS ... NEARBY
Mo ntvale, New Jersey 07645 Wherever you are in the United States, there's a nearby
Phone: 1 8002256 262 , ext. 7112 source of genuine factory parts for your customers'
e-ma il : StarTuned@mbusa.com Mercedes-Benz veh icles.
StarTuned is a quarterly publication of Mercedes-Benz USA, LLC (" MBU SA"). N o pa r t o f this news lette r may be rep rodu ced without the express written permission of
MBUSA. Ed i to r ia I and Circulation Offices: 598 Pine Po int Dri ve . Ak ron. Ohio 44333. Caution: Vehicle servicing performed by untrained persons could re sui tin se ri ous
injur y to t h ose pe r so ns or others. Informatio n contained in this news letter is intended fo r use by tra ined, pro fess iona l auto repa i r technic i ans ONLY. Th is
informat ion is prov i ded to i n form these tec hnic i ans o f co ndi t i ons wh i ch m ay occur in some ve hi c le s or to prov ide inform a t io n wh i ch cou ld assist
th em in prope r servic ing of th ese veh i c l es. Proper ly train ed tech nician s have til e equ i pm en t , t oo ls, safe t y ins truc tio ns, and k now-how to perfo r m repairs
correct ly and safely . If a cond iti on is desc ri be d, DO NOT ass um e tha t a topi c covered in these pages automa t ic all y ap pli es to yo ur ve hi c le or that you r veh icle has
th at condition. StarTuned is a registered trademark of MBUSA.
3. STARTUNED
Information for the Independent Mercedes- Benz Service Professional
February 2009 U.s. $6.00 € 1 2.50 Volume 9 Number I
Group Publisher Contributing Editor MBUSA Technica l Production Manager
Christoph er M. Ayers, Jr. Chip Keen Content Advisor Devon Ayers
cayers@cmacomm.com ckeen@cmacomm .com Donald Rotolo dayers@cmacomm.com
Donald.Rotolo@mbusa.com
Senior Project Director Contributing Editor Circulation Manager
Tamra Ayers Ke rry Jonsson MBUSA Project Manager Joann Turner
tayers@c macomm.com kjonnson@cmacomm.com Stephen Langelotti j turner@cmacomm .com
Stephen .Langelotti@mbusa .com
Editorial Director Contributing Editor List Consultant
Bob Freudenberger T Nash
om Art Director NFocus
bfreud@cmacomm .com tnash@cmacomm.com Jef Sturm
jsturm@cmacomm.com
5. Just like a blacksmith's bellows, the
Mercedes-Benz AIS "fans the flames,"
promoting rapid oxidation of pollutants
in the exhaust stream
Whether you believe technological the fire in the old two-way catalytic
developments are motivated by tightening converter. In th e early '80s when the
government regulations, or by the desire to three-way cat became popular, the air
add va lue for new-car buyers, there's no was piped into the cat downstream of the
doubt that they are coming along at an redu ction section after the engine warmed
ever-increasing rate. Secondary air injection up so that it wouldn't interfere with the
systems, however, have a long history - reaction that broke down NOx, yet was
they've been fighting air pollution since the available for the oxidation section.
1970s. Of course, they're way different today
from what they were then . Seltless
Originally, a belt-drive n pump forced air
in to the exhaust manifold to help oxidize A modern Mercedes-Ben z secondary AIS
escaping HC and CO. This was taken one (Air Injection System) does away with that
step further when that air was used to fee d energy-wasting and space-hogging belt in
On VB engines, the
secondary air system is
easy to test. Everything
is right in front of you.
Here we have the air
pump, shut-off valves
and switch-over solenoid,
all nicely accessible.
StarTuned 05
6. SECONDARY AIR INJECTION SYSTEMS
favor of an electrically-driven pump . Th is also
allows much more precise control of airfl ow,
which is necessary as emissions regulations
continue to become stricter on both federal and
state levels, and as the quest fo r improved fuel
efficiency continues.
The secondary air pump motor is only activat-
ed when the engine is relatively co ld - below 60
deg. F. It is only commanded on fo r up to two
and a half minutes. This is sufficient to warm up
the catalytic converters. The pump receives its
power supply from the secondary air pump relay,
which is operated by the ME contro l unit. The
system is also activated during closed-loop
operation, but on ly to test the system's abilit y to
pump air into the exhaust - the ME contro l unit
looks at the reaction of the 02 sensors.
There is one exception to th is rule. Early 111
Eva engines (four-cylinder supercharged) do not
use an electric pump. The ME control unit uses
On supercharged models, the the supercharger to genera te t he necessary pres-
sure/flow of fresh air to the exhaust. On models
compressor generates the air that is with an electronically-controlled "compresso r"
supplied to the exhaust ports through clutch, the clutch is activated at engine tempera-
tures below 60 deg. F., and can be kept engaged
this shut-off valve. Notice the solenoid
for about two and one half mi nutes . On later 111
mounted nearby that supplies vacuum engines, there is no supercharger clutch, so the
to open the shut-off valve. compressor is always spinning. The recirculation
flap is held closed to allow the compressor to
make the relatively sma ll amount of air pres-
sure/flow that the exhaust air inject ion requi res.
When the secondary air pump
motor is activated cold, or you cause
it to activate, you can measure the
amp draw of the pump. As you can
see here, around 26 amps should
be your reading with a normal
motor. If it is lower; the pump por-
tion is probably worn. If the amp
reading is too high (fused 40 amps)
the motor may be seizing up.
06 StarTuned
7. Your paid subscription to
www.startekinfo.com allows
you to pull up the wiring
diagram for the engine
management system. Look
at components K17 (relay)
and MJJ (air pump motor),
and you should be able to
come up with a diagnostic
plan to activate the relay
and test the air pump.
Shut-off valve stream, the 02 sensors register the high oxygen
content in the fresh air and this signal causes the
From the pump, the air is directed to a shut-off ME control unit to assume that the engine is run-
valve. This valve is vacuum-controlled, and is nor- ning lean . The ME's adaptation programming
mally cl osed to block exhaust gases from reach- tries to compensate for the lean condition by
ing the pump when the system is not energized. adding fuel. The ME looks for a lambda value
On four- and six-cylinder engines, there is only change of 25%. If the change is less than 25%,
one shut-off valve, but there are two on eight- the control unit determines that there is low flow
and twelve-cylinder models. When the system is of the secondary air injection system and flags a
active, a switch-over solenoid supplies vacuum to code of P041O, or one of its variants. This could
the shut-off valve(s) . This solenoid is ground-con- be caused by no voltage to the secondary air
trolled by the ME. Remember, with engine tem- pump, or a weak pump. An inoperable switch-
perature below 60 deg. F. the switch-over sole- over solenoid or a stuck shut-off valve can also
noid is grounded, which supplies vacuum to the cause codes. If all these components are func-
shut-off valves, opening them. Air is then sup- tioning properly, you may still have the problem
plied to the secondary air passages cast into the of blocked passages in the cylinder heads. How
cylinder head and exits into the exhaust ports. are you going to determine what's at fault?
This oxygen rich air mixes at the earliest point
with the hottest exhaust gases and promotes Codes and testing
continued combustion. The heat generated from
this process in the exhaust manifold heats up the Since problems in the secondary air system
catalytic converter fast and therefore reduces usually do not cause drivability symptoms, you
overall emissions quickly. will probably be diagnosing a code in the P0410
:JIII._ Being an emissions control system, AIS must range. The customer will more than likely bring in
have self-diagnostic capabilities. So, has its own the vehicle with a CEl (Check Engine light) or
monitor. Both the secondary air pump and the Mil (Malfunction Indicator lamp) on. You are
switch-over solenoid are activated during a nor- going to have to test components, and you are
mal drive cycle. Once the pump supplies fresh air going to have to start somewhere. Having a
through t he shut-off valve into the exhaust Compact III or Basic is a tremendous help when
StarTuned 07
8. SECONDARY AIR INJECTION
it comes to diagnosing any prob lem with a
Mercedes- Benz system, but we believe you
need to back up any scan tool diagnostics with
direct component testing for verifica t ion.
--..,.,,-- Testing the pump is fa irly simple. Remove the
engine covers and provide power to the motor
connecto r. You shou ld hear a loud whirring
noise. Whenever you compress air, even though
fi ltered, you are going to condense water, espe-
cia lly in high-humidity climate s. Thi s moisture
can get into the electrica l portion of the motor
and ca use failures . Th is is why the motor is
usually mounted on the engin e. The heat
shou ld cause any bu ilt-up moisture to evapo-
rate. The current draw of a good pump w ill be
25 to 26 amps. Any lower and you're probably
not pumping much air, and anything higher and
The switch-over solenoid receives
the motor is sta rting to se ize . manifold vacuum, and, when
:::!I._ If you are lu cky enough to have the vehic le
energized, directs this vacuum to the
overn ight, you can ve rify the air pump relay
operation. The pump power supp ly wire should shut-off valve. You can energize this
see battery vo ltage within a few seconds of a solenoid through the SDS software in
co ld start. This vo ltage can remain on for up to
150 seconds. If vo ltage is low or not there at your Compact III, or simply ground it
al l, yo u will need to locate the secondary air with a test light and check for vacuum
pump relay. You can manua lly ground the relay
and see that volt age is supp li ed to the pump. at the shut-off valve.
With a pa id subscription to
www.starteki nfo.com. you can retrieve a wirin g
diagra m for the veh icle and component loca- What does the 02 sensor say?
t ion usi ng Star Finder. As mentioned earli er, the
relay is contro ll ed by th e ME. With your To test the shut-off va lve, you can app ly
Compact III or Basic, you can command the vacuum to it with a hand-he ld vac uum pump - it
re lay on even if the engine is already warmed shou ld hold. How wi ll you verify that it is actually
up. Or, you can apply a test li ght to the ground open? You cou ld remove and phys ica ll y watch fo r
contro l of the relay. You shou ld hear the relay movement, but there are better methods. You
click and the pump run . Th e current draw of can app ly vacuum to the va lve and watch the
the relay is around 100mA. If th is is not the front (upstream) 02 senso r signa l. It shou ld drop
case, ve rify that you have vo ltage to both the to 0 mV with the secondary air pump command-
control coil and switched circuit of the relay. ed on and vacuum appl ied to the shut-off va lve.
- - -- If everything so far is in work in g order, you If the 02 sensor reads a lean condition, but does
will want to test the switc h-over so lenoid and not drop to zero, you can assume that the
shut-off va lves. The soleno id va lve is contro ll ed shut-off va lve is work ing, but there may be an
by t he ME, so the Compact III or Basic scan additiona l prob lem. Th e ME contro l unit looks for
too l will be ab le to activate the so lenoid, or you the Lambda (fuel trim) reading to compe nsate for
can once again manually ground the so lenoid the fa lse lean cond ition by add ing 25% more f uel.
with a grounded test light whi le the engine is If the secondary air passages are clogged or
runn ing. Yo u should measure manifold vacuum restricted in the cylind er head, the 02 sensor wi ll
at the shut-off va lves. not see the false lea n cond it ion and as a result
08 StarTuned
9. You can apply vacuum to
the shut-off valve and see if
it holds. This should also open
the valve. If you remove the
hose from the air pump motor
you should fee l exhaust
coming out of the valve while
the engine is running.
' - -1111111 -lolxI II6lilil the ME wi ll set a code for low secondary air flow.
Vehicle
~- ... ontrol unit I This is one of the more difficult problems to
IModel ! MEl IA c t iva t ions
~'
R AIR pump repair. Short of removing the cylinder head for a
m- AIR pump
~
~
~
t99
025 voltage
r ig h t
Ie f t
.mv
S tOFF
mV
I thorough cleaning, you wi ll have to find a way to
clear the carbon bu ilt-up in the intake passages.
C:: =. _ With a little luck and some good chemicals you
~
- 7t-
1
025 vol tage drops
below 40 mV wi t hi n
r---- may be able to clear the passages in the cylinder
~
170 ( 38-p ~~ynds?Fl
N <ltI FF
I--
- -
-
-
head without removal. Remove the shut-off
?
va lves and pour a reasonab le amount of cleaning
solution down the ports . You can remove the
exhau st manifolds and plug off the secondary air
ports, but this is not necessary. You will have to
!J ~
~ fWiiil
~ 1J !J
. let the cleaning solution sit over night. It also
make take a few appl ications before the
passages are clear, but after softening up the
Using your Compact III or Basic carbo n in the ports, apply shop air pressure to
the shut-off va lve exhaust ports and you shou ld
scan tool, you can perform a be able to open up the passages. If not, the
secondary air ~ow test while cylinder head wi ll need to be removed for better
access to the ports.
the engine is running. Even on
older vehicles such as this I 29 You can do it
chassis, you can use the HHT
Although pol lution contro l devices add com-
software to command the plexity to an engine's air/fuel/ignition manage-
secondary air system on and ment system, the above shou ld serve to illustrate
that as long as you understand how any part of
see the reaction of the 0 2 that system works, you can follow a logica l
sensors. process to come up with an accurate diagnosis .
That capabi lity wil l make yo u popular among you r
custo mers. One more thing: Think about adding
the pa ssages of the AIS to any ca rbon-cleaning
service you offer.
StarTuned 09
10. FEATURE ARTICLE
Mercedes- Benz vehic les have always had some uni que features . Along
with reliability, longevity, safety and performance, they've hel ped make
these engin eerin g masterpieces some of the most sought-after ve hicl es in
th e world.
One unique feature introd uced in the 1960s is the pneumatic centra l lock-
ing system, wh ich, as the name imp lies, does not use the electro-mechanical
actuators othe r manufacturers emp loy. In stead, it uses a co mbination of vac-
uum and pressure to move the door lock actuators quietly and dependably. It
has with stood the test of t im e and co nt inu es to this very day. As with any
unique system, however, there is a certa in leve l of fa milia rity that is neces-
sary in order to diagnose and repair the system.
10 StarTuned
11. Histo rical Perspective
Th e ea rliest reference we can find to pneumatic centra l locking in
Mercedes-Benz arc hives is from over 40 years ago. Back then, engin e
intake manifold vacuum stored in tanks did the lock in g, but the system
soon evo lved to use comb ination vac uum /press ure pumps to supp ly the
force needed. From 1983 onward, the change from vacuum to
pressure is accomplished by electrically reversing the rotation of the motor
- negative contro l vo ltage for vacuum, pos itive for pressure. Previously,
this had been done by means of a switching va lve . A typ ica l pump, by the
way, shou ld produce .5 Bar (7 psi) with in two or three seco nd s.
StarTuned I I
12. PNEUMATIC DOOR LOCl( S
With a paid subscription to
www.startekinfo.com. you
have access to W/S
~1IlJa.otP"''''.
Doe ,no QTIIO.2O+OQOS.01. PtIgI t ot '
(Workshop Information I o".m'"' L_ _
System), which will allow
you to pull up on
operational schematic of
the central locking system.
This shows all the PBO,1(J.204 1·09
components involved in AV 1
As/1
A2dl1
2 Top 199( wmdON antenna ampliflof
Remote control key
Lell fronl door fR receiver
N 1043
N6911
N6912
Reaf SAM control module
Loti front door con/rol module
Right lront door control module
fV13
SOOIf
Electronic ignition switch con /rol
module
Left fron l door lock SWitch (CA 8
<D (valid for Jeft-hand steer/no)
commanding the PSE mod- I A26f2 Right front door fR receiver N10 Overfle8d con/rol panel control
CD
A37 PSE control module (combined) module
. 581/1 Rk,Jht front door lock SWitch (CA
/._ /"" ... . . _ ..... ,.. .......>-...1_ •
ule to lock/unlock the doors. SIIHcIH ~OO SE CI65OO1C L 600 '.m 211),175 EnoineM "ueo
Press ure in the system is relieved in 15 to 20 seconds one quick tip, however: If th e veh icle has an EDW
after the pump stops . If there's a heavy leak, the alarm system, you can disconnect the intermediate
electronics that contro l it switch it off in 2 5 to 60 plug of the EDW cab le harness from the connector
seconds. (M14/1x2, or M14/2x2) and connect the central
Since about 1986, most M-B cars have had what's locking cab le harness directly to the supp ly pump. If
called the "multi-point" (also called "3- Point") system. ce ntral locking works okay now, it's time to delve
If you 're not sure what you're dealing with, go to the into the EDW.
passenger's door and unlock. If all the other doors do
the same, yo u' ve got multi-point. If not, eith er you're PSE Modern System Operation
working on a car with the old er single-point syste m
(which unlocks on ly from the driver's door), or there's At the heart of the centra l locking system is the
a problem. But since yo u' ve been presented with a pneumatic control unit, which is in total control of
compla int about this feature, you may be unable to the pneumatic portion of the system, and the vac u-
get any action out of it whatsoever. That means um/pressure pump is mounted in side it. It also
you've got to dig deeper. plays a role in operating the Clos ing Ass ist (CA).
Around 1990, IRCL appeared, which meant the The PSE module is usually mounted under the rear
locking function cou ld be operated by either the door seat on sedans and in the trunk on smaller coupes.
lock switches, or an infra-red remote. The PSE As the PSE module evolved, so have its inputs -
(Pneumatic System Equipment) modu le received all of
the in puts and outputs to command the door locks.
By '96, tne door switcn contacts were elimin ated, and
C::_. more than just direct switch inputs command it.
Nylon hose is used to connect all of these com-
ponents and route vac uum and pressure through-
the RCL (Radio Central Locking) module took control. out the centra l locking and clos i ng assist systems.
l:1li._ The integration of centra l locking with anti-theft and These hoses direct vacuum/pressure from the PSE
modu le to the individual door lock actuators. They
remote contro l systems evolved as the years went by,
and is quite complex with dozens of variations. Since have a single port on one side of a diaphragm.
a magazine article cannot possibly provide all the Supplying vacuum to it moves the actuator to
details, you will definitely need www.startekinfo.com. either the lock or unlock position . Supplying pres-
and WIS for specific information on the model at sure to the same port does the opposite. As you
hand. Here, we will cover the basic principles and sig- can imagine, this needs to be a "closed" system .
nificant addit ion s to give you a roadmap . We 'll offer Any leaks can cause malfun ction.
12 StarTuned
13. I~ hF8np" ii HHlWIN I!II:lEl ... C:'I" ~
Your Compact III or basic
Vehicle ontrol unit I
scan tool can access
rcurrent PSE Functions
data that includes version
IFilter stal I---::---:!C:-o-n~t-r-o-:-l-m-o-:-d-u':"'"1e-v-e-r-s""'i'-o-n--l
DTC memory
Actual Values 0245458532 - ./-
identification, diagnostic
Version coding
trouble codes, actual values,
actuations and coding.
This is an excellent way
diagnosis
<lIt~
to check multiple switch
inputs, even those from
other control units, without
having to test each
individual circuit.
---"_ _ As mentioned, from the early '90s the PSE module
received all of the inputs and outputs to command
the door locks . Starting with the early versions, one
of the basic commands to be seen by the PSE mod-
ule are those from the left and right door switches,
which are within the pneumatic actuators. Rotating
the key in the door lock or actuating the lock button
atop the door signa ls the PSE. There is one switch
conta ct for the lock command and another for
unlock, and they are wired together with the trunk
lock switch. Any of these inputs can switch the signal
voltage of the PSE module to ground. When the mod-
ule se es t his, it wi ll eith er lock or unlock the doors .
There are other switched inputs, but most of them
are for determining door and trunk latch positions .
...-- - - Later PSE modules have self-diagnostic capabi lit ies .
It can store codes and data even with systems as far
back as HHT, which is incorporated into the Compact
III SDS system. You can see multiple switched inputs
at a glance. You can monitor the lock and un lock
command switches in each individual latch, trunk By monitoring the SN I and SN2 signals,
tumbler, trunk lid position, individual door position
and inte rior CL switches. Since there can be varia- you can evaluate the command to the
t ions dep ending on veh icle options, the PSE module PSE module to both lock and unlock the
needs to be version coded if replaced. Some vehicles
have CA (Closing Assist), others have RCL (Remote doors. You do not need to use an oscillo-
Central Locking) or CF (Comfort Lock system) scope to monitor these signals. A DMM
options.
C _ _ If the vehicle is equipped with Infra-Red (IR) remote will work fine. You are looking for a I 2V
controls, there are some differences in the way the signal on each of these wires.
StarTuned 13
14. PNEUMATIC DOOR LOCKS
system works. The basic door lock/ unl ock switch Testing the System
signa ls are supplemented with door switch com-
mands referred to as SN1 and SN2 signa ls, wh ich
C=-_ If the pneumatic central lock ing system is not
function in g properly, one of the first steps is to find
originate in the Remote Centra l Lock ing (RCL) mod-
out if there is a problem with the pneumatic system -
ule. Either can co mmand the doors to lock/ unlo ck.
the vacuum/pressure pump, nylon lines, or any of the
By '96, the door switch contacts were elimin ated.
three to five actuators - such as a leak, bind ing, or
The RCL has taken ove r for these manual contro ls.
seizing. This can be done fairl y easily at the PSE
This means the RCL is in control of the door locks
con trol module . You will notice a single large line
and the signa Is to the PSE module have to be tested
in order to determine if the PS E is work in g. These com ing out of the module and feeding one of two
SN 1 and SN2 signa ls are also passed on to the ATA
(Anti-Theft Alarm) system to confirm that an accept-
able remote opened the doors before the engin e is
all owed to sta rt (as of '98 w ith SmarKey, engi ne
start ing is a sepe rate function fro m CL and ATA).
Knowing th is can be helpful in diagnosing the PSE
function if it is not work ing. Open the driver's side
window, close the hood, trunk and all the doors.
All ow the vehicle 's alarm to arm itself. Then, use the
remote to open the doors. If the doors do not
unlock, reach in thro ugh the win dow and try to start
the engine. If it starts, you know the RCL signal
made it to the ATA mod ule and therefore must have
made it to the PSE mod ule. Th e module sho uld have
unl ocked t he doors. If the engin e does not start, you
may have a prob lem with the RCL system. Monitor
the vo ltages on SN 1 and SN2 and see if th e 12V sig-
nals get pulled to ground for eith er t he lock or
unlock command.
c:z_ _ A later evolution of the system is the Conven ience
Feature (C F). This integrated the operation of many
body contro ls into one contro l unit, in cluding power Looking at these signals on a dual
windows, power door locks and power slidin g pop-up
roof. The CF contro l unit directly contro ls the win- trace scope allows you to see the lock
dows. Door locks are sti ll controll ed by t he PSE unit, command (upper trace) and unlock
but it receives commands from either the door
switches or t he CF contro l unit. After '96 when the command (lower trace). As you can see,
door switches were eliminated, the Drive the I 2 V signal gets pulled to ground
Authorization System (DAS) radio frequency/Infrared
(IR) contro l module took over command ing the PSE when the door locks are actuated, in
unit to operate the power door locks. this case by the RCL unit as the remote
CII_ _ Another feature close ly related to the PSE system
is Closing Assist (CA), wh ich uses its own separate button is pushed to open and close the
co ntrol unit that is referred to as the CA supp ly doors. The signals are there, but the
pump. It is only used for lock in g, not for unlocking.
The goal is to continue to close the door all the way pneumatic pump did not turn on.
after latc h con tacts the door j amb. A door micro- At this point check for powers and
switch ind icates whe n the door is alm ost closed and
th is signals the CA system to supp ly vac u- grounds to the PSE unit. If they are
um/pressure to the CA actuators in the door latch good, replace the PSE module.
assemb lies .
14 StarTuned
16. FEATURE ARTICLE
Mercedes-Benz timing chains and
tensioners lost and lost. But, given the
tremendous number of miles people put
on these vehicles, they will need attention
sooner or later
1 Stal-Tuned
6
17. tion of Timing
In order for a four-cycle engine to work, marginal, and making replacement at regular
there must be precise coordination among the intervals necessary. On the other hand, in a
intake, compression, power and exhaust strokes . properly-maintained vehicle timing chains and
Advances in engine technology have helped related hardware can last well over 200,000
increase performance throughout the rpm range. miles. Eventually, however, wear will reach the
Variab le intake manifold runners optimize air point where diagnosis and replacement wi ll be
inta ke velocity, variable valve timing has broad- needed, so you have to know how to perform
ened the power band, and variable lift the job properly. This is usually not too difficult
further fine-tunes air intake and exhaust flow a task providing you had the correct tools, and
for even greater performance, efficiency and any shop specializing in Mercedes-Benz
economy. Regardless of how high-tech intake vehicles should have such items as a chain
and exha ust events have become, maintaining pin remover/installer.
basic cam/crank timing remains essential.
First Scenario
Keeping Time
_ _ _ Typically, you will need to deal with the timing
Mercedes-Benz vehicles have always chain because of noise from a stretched chain
excelled in sound engineering and reliability. or weak tensioner, or because the cylinder
From Formula 1 to Indy cars, Mercedes-Benz head must be removed for whatever reason.
engines have always been in the top tier. The Either way, the timing chain has to be removed
same engineering principles that are used to and put back into proper synchronization upon
create a reliable ra ce engine are also used for reassembly. In the case of noise, the job is not
production vehicles. One steadfast belief held by as daunting as you may think. Mercedes-Benz
the company's engineers is in the reliability of has service procedures that make this a rela-
the timing chain. The valve trains found in large tively simple task. Many Mercedes-Benz
six cylinder, V8 and twelve cylinder engines engines have the timing cover cast as one unit
natural ly have more mass to move than those of with the block, so the cover cannot be removed
little fours. This puts undue stress on the to access the timing chain.
camshaft drive mechanism, making a timing belt
Continued on page 20
StarTuned 17
18. R EP LA C E - We replace more parts than aftermarket brands.
E NG I NEE RED - Designed to meet original OEM drawings.
M AN U F"ACTU RED - Made with same OE components as factory parts.
A ss EM B LED - Completely assembled from components and not just repaired.
N EW - Tested to new unit standards.
QUALITY, RELIABILITY AND VALUE
The quality, reliability and value of the Genuine Mercedes-Benz Remanufactured
AIC Compressor wasn't meant to be taken lightly. It is not only an exact replacement
for the original unit, it's also remanufactured and tested to meet the same strict
specifications as the original, so it performs just as well. And like all remanufactured
parts, it's covered by the Mercedes-Benz limited parts warranty.* In fact, the only detectable
difference you' ll find between a Genuine Mercedes-Benz Remanufactured AlC Compressor
and a new one is the price. Which we're sure you'll find quite refreshing.
IT'S ALL I N THE PROCESS
Remanufacturing Process (Genuine Mercedes-Benz)
1. Dismantle core 2. Replace key 3. Test all 4. Replace
and clean all , components 100% other critical components that
components. with new OE part. components. do not meet specs.
Rebuilt Process (Typical Aftermarket)
1. Identify damaged 2. Replace damaged 3. Re-assemble,
part or parts. part with non-OE test and box.
part and clean.
*See your Mercedes-Benz dea ler for details and a copy of the Mercedes-Benz Spare Parts Limited Warranty.
20. A QUESTION OFTIMING Continued from page 17
lnf~bOXl UIII'MI ~ A8BY9T
Your paid subscription to
~~~ ~~~~~~~____~_________________
'''==
"hm ".=1
~ ,.g' ../../- www.startekinfo.com will
Ooc .m. ~"05~~~.!601~V'
s...~mcdt
P,g,'
SI ...... al ... dl
: allow you to access WIS
3 Remove the rags trom the ~mln~ case recess
documents. Here the correct
rn Otherwise. they could get pulled into the liming csse reCaSS
I'otlen the engine Is cranked.
step-by-step procedures are
4 Tum £t1e crankshaft slOVi1y In the engine's dlraction of rOfa~on
(arrow) and draw In the newtlmlnr;; chain (2) unbl the ends of the
new timing chsln (2) canbe connected.
rn flJ:, the new ~ming chain (2) is being dravm In (arrows). pull
laid out for you. You are also
out tne end oflhe old timing chain ( 1) evanly as Itbecomas tree.
5 Cover over bming case recess WIth e clean clotl'1
linked to pages that let you
rn The dmlng case rscess must be secured against parts failing
down Parts that have lellen into the timing case recess must be
removed
know what special tools you
6 ISJOetach the assembly link (01). and separate the old timing
chain (1) from the new timing chain (2). will need. The procedure for
m assembly link (01) must be remov.;.d The assembly link
The
Is only en aid for assembly and Is nol suitable lor engine
operation
. '--~------.-'------"--.-
drawing in the new chain IS
pictured here.
: .. _ There is a straightforward procedure, however,
that makes replacement possible anyway. The
first step is to remove the valve covers. Also
remove the spark plugs to make it easier to turn
the crankshaft by hand. You may want to start
with the engine at TOC, it's not really necessary.
In most Mercedes-Benz "Checking Engine
Timing" procedures, you are asked to rotate the
crankshaft to a specific point on the pulley. This
is usual ly not TOC, but a specific degree mark
past TDC . If yo u are so inclined, you can apply
paint marks on the cam gears and adjacent
marks on the timing case cover to check your
work once you have changed the timing chain.
: :B! iI. _ The next step is to use the cha in separating
tool to force out the two pins of one outer link.
This will break the chain and leave two sid es of On this III engine, if the camshafts
inner lin ks exposed. Install a service master link
on the chain leading into the upper portion of the are in their home position you will be
engine. Use one pin to attach this link to the able to install a com positioning tool
upper side of the chain currently installed in the
engine. Connect the other half of the service in the bocks of the com sprockets.
master link to the new replacement chain. You The screwdriver indicates the loca-
should now have one long continuous chain half
installed in the engine . Grab the lower half of the
tion of one of the holes (intake
old timing chain coming up from crankshaft com). Notice how the intake and
toward the passenger side camshaft and pull.
While doing this, rotate the crankshaft pulley
exhaust com lobes are facing one
clockwise. This will draw in the chain. It is critica l another. This gives you a ballpark
not to rotate the engine counter-clockwise at any ideo that you have the timing close.
po int in the repair. If you do, the chain tensioner
20 StarTuned
21. " ..
' -
~ - ·_shouid-the;:g9mg~~tg . li~et911gh:.~·-: =_~:
- - -' , -:, - ', ' ~',' ..-~,:.:,-.","-~", ' ,•. - ".::~ ::.- .. - - .---
Small scratches, stane impacts, dents and blemishes -
and the custa,mer's Mercedes can quickly lase the shine
fram its exteriar.And because that is annayance enaugh,
we keep th e casts far a reprir fS ,lo'y; ~:s passible - with
Mercedes-Benz Small Repair. Speci'~(i:~paiX rpethads mean
that small appearance defects vanish in nexft6 na time.
It gaes withaut saying that .our kits meet the high, tested
Mercedes-Benz quality standards that yau expect. Sa if yam
custamers are driving araund with a small imperfectian, it
may be able ta be repaired with Mercedes-Benz Small
Repair. Small Repair Kits are available fram yaur authorized
Mercedes-Benz dealer.
Training an the Small Repair methad s are available fram
Reliable Autamative Equipment. Please cantact Reliable
Autamative Equipment ta inquire abaut training yam
staff ta perfarm these repairs quickly and efficiently.
RAE
RELIABLE AUTOMOTIVE EQ1JIPMENT, INC. 1.800.328.7855
StarTuned 21
22. A QUESTION OFTIMING
Look at the intake com
on the right and you can
see the camshaft timing
adjuster. Since the engine
rotates clockwise, you
need to turn the adjuster
counter-clockwise all the
way until it stops, then
engage the timing chain.
wil l co llapse and probably all ow the cha in to In severe cases, this can snap off a cam
j ump teeth on one of the sprockets, thus throw- sprocket! To reset the tens ioner, remove the cen-
ing off valve tim ing. If you continu e to rotate th e ter cap with a hex key socket, and the pre-load
engine clockwise you will eve ntually draw in the spring wi ll fallout (watch out for the alum inum
entire section of new doub le-ro ll er cha in and sea lin g washer). Th ese are hydraulically-assisted
Wl._
once again see the service master link.
At this point, you must remove the service
master link as it is onl y intended to be used dur-
tensioners that require engine oil pressure to add
tension as engine rpm rises. Th e pre-load spring
pushes on a piston that in turn pushes on the
ing service . Install the permanent link with a chain tensioner guide. The piston ratchets
chain link pin installer. The tensioner may be outward to apply tension. Once it ratchets out, it
pushing on the cha in hard enough as it comes wi ll not return even with the spring removed. So,
up from the crankshaft that the two ends won't remove the who le body of the tens ioner, pu ll the
meet. So, you can loosen the tensioner to help piston out and away from the pre-load sp rin g cap .
with the insta ll ation of the permanent link . Don't , -- ---, Now you can mount the body of the tensioner
take the tensioner out all the way as t hi s may into the tim ing case cover, making sure the
allow enough slack for the cha in to jump time. alum inum sea ling washer is properly installed.
The permanent link outer plates need to be Put the piston into the open ing of the tensioner
installed and a chain ri vet insta ller must be used body fo ll owed by the pre-load spring, then instal l
to sta ke down the roller pins just like those of the cap over the spring and thread the cap into
the other links. Rotate the engine severa l times the tens ioner body. Some force will be requ ired
by hand and watch for your paint marks to be to compress the spring, wh ich is necessary to
sure va lve timin g is correct. keep the chain tight enough for start-up. Once
~_. At th is point it should be safe to remove the the engin e is running, oil pressure does the job.
tens ioner and either insta ll a new one or reset the That's why it's important to replace both
old one. Resetting the tensioner is critica l. As you alu minum seal ing washers even if you're reusing
ran the new cha in in and the old one out, the the old tensioner. By the way, when ordering a
tensioner's spring pushed outward to take up the new tens ioner you shou ld be aware that it does
slack in the chain. If you were to leave it in this not come with the threaded cap, so you will need
position, the chain wou ld be far too tight. to use the cap from the old one.
22 StarTuned
24. A QU ESTION OF TI MING
access the crankshaft sprocket and you will also
have access to the chain gu ides . After removing
the tensioner, va lve coverts). cha in gu ides, cam
sprockets and oil pan, you wi ll be able to remove
and replace the unbroke n cha in. This procedure
also requires some special tooling since you have
to properly align the camshafts and crankshaft.
C:::_ _ Over the years, Mercedes-Benz has used sev-
eral different ways to assure that the camshafts
and crankshaft are prope rly synchron ized - too
many to be thorough ly explained in a magazin e
article. So, we will provide a simp le overview.
There are usually a few types of special tools to
lock down the camshafts. Some enter t hrough
the rear of the sprockets. An ali gnment pin pass-
es through a hole in th e cam cap and a ho le in
the sprocket. With variab le va lve timing comes
the important step of setting the intake cam
sprocket to the home position (retarded). Hold
the camshaft itself in the locked posit ion with a
wrench and twi st the camshaft adjuster in the
opposite direction of t im ing chain rotation, wh ich
Mercedes-Benz usually times its
results in the retarded position. If there is any
engines at a position other than question of a camshaft adj uster not moving
TOC. In the case of this I I I engine, freely, now would be the time to change it. The
use of non-approved oils in these engines can
the timing pulley should be set to cause sludge build-up and jamming in the
20 deg. after TOC. This puts the adjuster mechanism. Thi s can lead to misfires,
poor idle and the Mll/CE l com in g on . On newer
keyway in the crankshaft at just engines, special tools bolt down to the va lve
about the I2 0 'clock position. cover flange on the head, and tabs lock into the
cam sprocket, but these will be covered in future
Now, you should be able to line articles . Generally, the crankshaft is located a
up the cams. few degrees past TOC and is not locked down .
Closing Up
Second Scenario
With the timing chain and camshaft adjuster in
::::JI_ _ If more extensive service work such as a cylin-
the proper position you can start re-insta ll ing the
der head R&R is performed, it may be easier to
chain guides, oil pan, va lve covers and tensioner
simply remove the timing chain as one unit. Start
as outlined earli er. It is always a good idea to
by removing the tens ioner. You can then remove
rotate the engine by hand severa l ti mes to verify
either the camshaft timing sprockets, or the
all components are properly timed and that the
camshafts themse lves, depending on the particu-
chain meshes smoothly. The f inal step shou ld be
lar engine . For instance, on the M272 motor the
to install the spark plugs and fire up the engine,
timing chain on ly drives the intake cam, which
allowing time for oil press ure to reac h the
then drives the exhaust cam by means of gears.
tensioner before accelerating.
In th is case, the cams will have to be removed to
access the tim ing chain. Drop the oil pan to
24 StarTuned
25. A Mercedes-Benz should be true to its origins. So turn to the Mercedes-Benz Classic
Center for Genuine Mercedes-Benz Classic Parts. Their experts have access to over
40,000 true-fitting Genuine Classic Parts of the highest quality, plus a 12-month
limited warranty. They sell direct, ship direct and even assist In parts specification.
Mercedes-Benz Classic Center When you want authentic parts, only the source will do. MBUSA.com/ClasslcCenter
To speak with our Parts Experts, call our Parts Order Desk at 1-866-MB-CLASSIC (1-866-622-5277).
Mercedes-Benz Classic Center USA, 9 Whatney, Irvine, CA 92618
Call or vi sit for additional details and a copy of the Limited Parts Warranty. <02008 Mercedes-Benz USA, LLC
26. FEATURE ARTICLE / COLLISION REPAIR
The Straight & Narrow
When evaluating chassis integrity after collision damage you need to
take the extra steps to verify straightness. The inherent value of a
Mercedes-Benz vehicle definitely makes these extra steps worthwhile.
the next step is to look for indirect
Look at the collision industry Assessment or secondary damage that was
statistics co mpiled in the last few
ye ars an d you will notice an One of the first steps that is caused by this collision. Although
increase in vehicles defined as a often overlooked and/or taken for we realize this is not always t he
tot al loss by insurance companies . granted is the damage assess- case, it is often a good idea to
The reason for this is multi- ment. This is more than just a visu- start pulling the frame in a linear
fa ceted . Increases in the cost of al overview of the parts that will direction extending the body front
pa rts, the short age of certified need to be replaced. A deeper to rear. Pulling fron t to rear wi ll
body techs, and collision repair analysis should be incorporated "stretch" the chassis into a
fac ility tooling/environmental into the assessment. Look at the straighter position . Obviously,
compl iance costs have all con- point of impact and determine its with corners and angled frame
tri buted to the overall price of a direction. You should think like a panels this will not always be the
repa ir. Also, the vehicles them- detective at this point and try to best way to go, but it is a start.
selves often contribute to the recreate the accident in your head . Sometimes it is better to pull the
added cost. Exotic metals, con- It sounds like common sense, but framework at 90 degree angles to
struction welding technology and this usually gives a good indication the panel's original location . This
fastening techniques have all of what points you should start may take several steps as you
required retooling and training, pulling from . Also, this may be a change the location and / or the
wh ich adds to the overhead of any good way to gauge from what direction of the pull point to stay
col lision repair shop . Mercedes- direction you should start pulling perpendicular to the panel you are
Ben z vehicles, however, retain suf- once the chassis has been initially pulling. These are just some gen-
fi cient value to justify the cost of straightened. eral guidelines rega rding frame
repa iring most collision damage. Next, look for damage at the far- alignment meant to get you think-
Reputable shops know the thest point from the impact. This ing about the next step, which is
importance of returning the vehi- gives you the total surface area of developing a repair plan.
cl e's structu ral integrity to its pre- all of the damaged panels . Even if
collision state. When dealing with the damage in this area is minimal, Measuring Up
frame damage, it's essential to it needs to be straightened. During
the pulling process, it can be used An old adage says, " Before you
restore the basic framework for
as a gauge of the straightness of can go anywhere you have to
proper chassis dynamics (such as
the overall section. If the farthest know where you are ." The same
suspension alignment) and future
point of damage after pulling has can be said for frame straighten-
crash-worthiness . You may ask
now returned to its original shape, ing. This next step in the repair
yourself, "When should I check
you may want to start pulling from process involves measurin g
chassis alignment?" and, "How
another point. chassis alignment on a bench or
can I do a better job of pulling that
Back to assessing the damage, "jig" against Mercedes-Benz or
chassis into alignment?"
26 StarTuned
27. Vehicle Dody Informalion
lUrudn .£j.nz. vthld15' 9o!1)'andBodyl,lat.rlallnlollna~on
lor DodyslloP'. acclcl.nt UUUOI' alllllnlllram:.e camplnill
Men;cdcs-Benz 230
.....
Home
.~
'"
",
,~
'"
'"
'"
,,,
'" •
n
•=
,,,
M'"
at.rlel,
EIII/!pm.nI&TooI.
OM :ldS!(I(II · >300rl/ """'It"'~l.ttcnltn
•111&" ."1111,111 lie.! '" ~50 " /mm' !Cr.de wenltn
• LUlI'ts"'m
O Al~mlolUm
. PI.a"~1
IB Oala ShH I230
Bodyfuluru
Mod. rn hybf1 dbO"Ystructur, Intludlng hlgh-,ltenglh sin'. alum'num and mag onium
• D. bCl'llbl, !font and lUI modules ma~. bod:)' repair easltr
-----~-- -.. ~
Before you start the pulling process you need to know what met-
als you are working with. Mercedes-Benz uses different metals
with dif ferent strength levels to achieve structural strength and
occupant safety. A visit to www.mbcollisioncenters .com and
your membership gets you this important data.
Car Bench is a Mercedes-Benz approved alignment jig for frame
straightening. There are various models available, and by visiting
www.carbenchna .com you can arrange bench rental and download
measurement specifications.
28. COLLISION REPAIR / SUB FRAME R&R
!iil WISI.,RA no! " .. on, GJ@[gJ the frame until you match the
measurements. These measure-
ments are supplied by Mercedes-
Benz through WIS-Net, wh ich you
can access with a paid subscrip-
tion to www.startekinfo .com.
Aside from having the step-by-
step procedure to rep lace interior
body panels, it also conta ins
measurements for K-point frame
diagnostic procedures. If you
have a hard time locating the K-
point measurement spec ifica-
tions, try entering a chass is num-
ber or the entire VIN and look
under group 40.30.
Newer vehicles util ize a different
procedure: measuring off of an
alignment bench. Mercedes-Benz
With a paid subscription to www.startekinfo.com. you can use has approved two bench manufac-
WIS-Net to pull up the K-point measurement data. This infor- turers for chass is alignment, t he
mation is only used for diagnostic purposes, particularly on Car Bench, and the Celette chassis
older models built before the turn of the millennium. You can alignment bench. If you have
invested in the Celette or Car
use these measurement points to see how bad the damage is.
Bench jig, you can access those
the bench manufacturer's specifi- measurements from their web-
cations . Here is where a hard sites. The Celette website is
dec ision has to be made: Is the www.celette-us.com. On the home
f rame damaged beyond repair? page, select the "Fixture bench
No one wants to put in all the Setup Sheets" field, then select
labor to get to this point and not your model chassis. There may be
repair the vehicle. Tota ls should VIN number differences, so be
have been weeded out during the sure to select the correct identifi-
damage estimate. cation number. The Car Bench
On earlier Mercedes-Benz mod- website is www.carbenchna.com.
els (previous to the 210 chassis), From the home page, select
chassis damage was measured "Support," then "Resources."
Here is a Celette bench with
off of a K-point. That is, a point From there, select the "+" symbol
a 230 chassis set up for
within the driveshaft tunnel that next to the heading "Datasheets,"
measurements and pulling.
was hopefu lly the least likely to followed by the type of bench you
The framework setup and are working with, the manufactur-
be hit in an accident. The K-point
procedures are all available er (Mercedes-Benz), model and
is a diagnostic too l for body men
on the website. Remember, chassis variant if applicable.
to use to straighten frames. From
this K-point you measure the dis- you can use higher strength Rental units are available from
tance to all suspension pick-up steels to pull lower strength either manufacturer. These are the
points and see if the chassis has steel, but you cannot reverse two chassis alignment jigs official-
twisted. From here, you pull on the rule. ly approved by Mercedes-Benz .
28 StarTu ned
29. They inherited our strongest genes.
Not all remanufactured parts come from such hardy stock. re li abi lity. And they feature the same-as-new Replacement
Genu ine Mercedes-Benz Remanufactured Parts strictly adhere Parts Limited Warranty. Access over 700 parts in 20 product
to factory specifications - fo ll owing a uniform, precis ion lines for today's vehicles, and classics too. Offer your customers
process. In fact, all wear and tear parts are replaced with OE affordable Genuine Mercedes-Benz Remanufactured Parts.
pa rts - tested to OE specificatio ns - for higher qua lity and Visit mbwhelesaleparts.com or contact your dealer.
30. COLLISION REPAIR / SUB FRAME R&R
Bending To
Your Will
Once the chassis is on the bench Dor; . no. tr«I~~~!' ""'11' 1 01'
s..o._~ .. ","",
and the measurements have been
taken, you can start pulling. Frame 1 Position modular members on indelC tiekl15 end 21 3 Mount Mu~I·Z
on Side pbs (8).
alaments M.Z 260 (arrow points towards the Iront)
2 Mount side Jibs (8) on modular members.
straightening is an art developed 4 Insert cy~ndrical supports (10) Into Ml 260 (upper hOle)
through experience, but there are
some relatively new concerns with
Mercedes-Benz designs and metal
composition . In some cases, of
course, the damage to a panel will
be so great that straightening may
not be the best option compared Fasten longiludln~1 portel member (9) at cylindrical supports
with bolts M12 >:35 (11 2 and 8)
6m
m
...-
lI the rear lender Is removed,
nLr~~r 'QnnQr l
Insert spacer (dj (Shael lniCkness
to rep lacement. In the case of
high-strength steel, this becomes
a requirement. High-boron steel is With your paid subscription to www.startekinfo.com. you can
very difficult to reform after crash access step-by-step instructions for alignment bench assembly
damage because it is so strong. and measurement procedures. You also are provided with
Mercedes-Benz uses fou r grades replacement procedures for interior structural panels as well
of steel: mild steel, high-strength as exterior body panels.
steel , modern high-strength steel
and final ly ultra high-strength virtually impossible to reform and strength steel and weld or bond
steel. Mild stee l is much easier to will need to be replaced. When and rivet in the new sections. In
pul l. The higher strength steels can damage is localized, it is much the case of the 215 chassis, you
be pul led, but often return to the easier to cut out the damaged sec- have to be even more carefu l
pre-pulled shape . Ultra high- tion and replace it. pulling panels since high-strength
strength steel is heat formed, so Ultra-high strength steel is more steel and mild steel is mated with
without extensive equipment it is widely used in new Mercedes- aluminum structural panels. On a
Benz chassis such as the 204, 216 positive note, when pulling alu-
and 251 , and to a lesser degree on minum Mercedes-Benz always
the 164, 171, 211, 215 and 220 recommends replacement over
chassis. The 216 chassis has repair work.
incorporated even more higher-
strength steels than other
Mercedes-Benz models. When
In Conclusion
pulling ultra high-strength steel, it Your extensive experience as a
will obviously react differently body man will serve you well while
from modern high-strength, high- assessing the damage, measuring
strength and mild steel. The key the alignment points and during
point to remember is that you can the actual pulling procedure.
Here is a frame attached to use higher-strength steels to pull Simply keep in mind the
the bench. Points on the and align lower-strength steels, Mercedes-Benz recommended
chassis can be measured but you cannot do the opposite for procedures outlined in WIS-
from here, and you can start obvious reasons. You will simply Net and the knowledge of the var-
the pulling process. On this deform the lower-strength steels ious metal compositions of the
230 chassis, you need to be in the process. Use ultra high- chassis you are working on should
aware of the different metals strength to pull the chassis, then yield a structurally-sound and trou-
and their relative strengths. cut out the sections of ultra high- ble free-repair.
30 St arTuned