Mercedes-Benz Service

Electrical Troubleshooting Manual @Model 201 Model Years 1984 - 1993

Mercedes-Benz of North America, Inc.

s-2372-092

0 19xx Mercedes-Benz of North America, Inc.

Mercedes-Benz Canada, Inc.Service and Parts Literature

All rights reserved. Reproduction ortranslation in whole or in part is notpermitted without written authorizationfrom the publisher. Reprinted 1992.

Published by Mercedes-Benz of North America, Inc.

Printed in the U.S.A.

Order no.: s-2372-092

INTRODUCTION

This manual contains schematic diagrams and component locations for models201.024/028 (190 E 2.3), 201.029 (190 E 2.6), 201.034 (190 E 2.3-16), 201.122 (190D 2.2), 201 .126 (190 D 2.5) and 201 .128 (190 D 2.5 Turbo). Also included isinformation on: How To Use This Manual, Symbols, Troubleshooting Procedure andAutomatic Climate Control.

The index for schematic diagrams appears on page 101.The index for component locations appears on page 201.The index for Tempmatic Climate Control appears on page 301.

Schematic diagrams should be referred to when diagnosing a problem (seeTroubleshooting Procedure).

The information contained within this manual is accurateto the best of ourknowledge at the time of printing. All rights are reserved to make production, designand specification changes at any time without notice and without obligation to givenotice. Any such changes will not be contained within this manual

It is a general assumption that the reader is familiar with basic mechanical andelectrical repair procedures and Mercedes-Benz vehicles.

Mercedes-Benz of North America, Inc, assumes no liability for any damage toperson or property caused by the utilization of this publication to effect maintenanceor repair work on Mercedes-Benz automobiles.

Mercedes-Benz of North America, IncService and Parts Literature

How to Read Schematic Diagrams

Electrical components which worktogether are shown together. Schematicdrawings are arranged so that currentflows from positive at the top of the page,to negative at the bottom. Fuses areshown at the top of the page. All wires,connectors, switches, and motors areshown in the flow of current to ground atthe bottom of the page. The “hot” labelsappearing at the top of fuses or compo-nents show the Ignition Starter/Switchpositions which supply power to the point.(See Circuit Identification, page 9.)

The terminal number “30” appearingon the Ignition/Starter Switch and Exte-rior Lamp Switch means that theseterminals are a lways suppl ied wi thpower. The terminal number “15” on theIgnition/Starter Switch means that thisterminal is supplied with power onlywhen the Ignition/Starter Switch is inthe “Run” or “Start” positions.

Component and Wire Representation

All wiring between components isshown exactly as it exists on the vehicle.Wiring inside complicated componentshas been simplified to aid in understand-ing their electrical operation. Tran-sistorized components are shown as plainboxes labeled with a solid state symbol.Switches and sensors are shown “at rest, ”as if the Ignition Starter/Switch were off.Notes are included which describe howswitches and other components work.

Circuits Which Share Powerand/or Grounds

Each circuit is shown completely on oneschematic diagram. Wires common to dif-ferent schematics are cross referenced andmarked with arrows. To find other circuitswhich might share fuse terminals or screwterminal blocks, look on the Power Dis-tribution or Fuse Block Details schemat-ics. To find other circuits which mightshare connections to ground terminals,look on the Ground Distribution schemat-ics.

Power Distribution and GroundDistribution Diagrams

The Power Distribution diagrams showconnections from the Battery and Alter-nator to the fuses, and to the IgnitionS t a r t e r / S w i t c h a n d E x t e r i o r L a m pSwitch. This will tell you how each circuitgets its power, and what circuits sharecommon fuses. Ground Distribution dia-grams show how several circuits are con-nected to common grounds.

Component ldentif ication

Component names are found underlinednext to or above each component. Abovethe component name, you will find aComponent Identification Code Number.

d REVISIONS:

SYMBOLS

ONE POLE,TWO POSITIONSWITCH

SWITCHES THATMOVE TOGETHER

OASHEO LINE SHOWSA MECHANICAL

m CONNECTIONBETWEEN SWITCYES

X28

GO CONNECTIONS (PINS)IN THE SAME CONNECTOR

COMRINENT W I R E I N S U L A T I O N

I/ IDENTlFlCAtlON

CODECRT- - NAME OF COMPONENT

75 BRiVL CON\NECTOR\

DETAILS ABOUTTERMINAL COMPONENT ORNUMBER OPERATION

zSCREWTERMINALBLOCK

1.5 RO s BU

I I

DASHED LINE SHOWSPARTS OF THESAME CONNECTOR

TWO PARTSOF THESAMECOMPONENT

RELAY SHOWN WHEN COIL ISWITH NO ENERGIZEO. SWITCHCURRENT IS PULLED CLOSEDFLOWING

m THROUGHCOIL

TWOPOLE,FOURPOSITIONSWlTCH

THE DIRECTIONOF THE ARROW

WlRE SIZECONVERSION CHART

METRIC AWG:ROSSSLCTlONALAREAlNYY *I IAMERICAN WIRE GAUGEI

.5 2015 18I 161.5 142 142.5 124 106 88 8I6 420 425 232 2

OTHER CIRCUITSALSO GROUNDAT Wl

IGNITION/STARTER/

GROUNDS

IN ACCV. RUN OR START i”l

R E V I S I O N S .

SYMBOLS

q ENTIRECOMPONENlSHOWN

r-1 PART OF AI

I1 COMPONENT; SHOWN

L-J

COMPONENTWITH SCREWTERMINALS

CONNECTOR ONCOMPONENTLEA0 IPICTAILI

E Gh

CONNECTORATTACHE0 TOCOMPONENT

l-l COMPONENTCASE ISOIRECTLVATTACHED TO

_= METAL PARTOF CARIGROUNOEO)

IL, i T E R M I N A L S

INOICATES THAT FUSE 4

j p&dL -__-J

INOICATES THAT FUSE 4IS SUPPLIED WITH POWER

J WITH THE IGNITIONSWITCH IN THE RUN OR

r START POSITIONS

I

IL

WIRE CHOICESFOR OPTIONSARE SHOWNAN0 LABELEO

5 GVI /M A N U A L A U T O M A T I CTRANSMISSION TRANSMISSION

I

I 1\

15 RO 5 cv

I CONNECTOR REFERENCE

5 BK NUMBER FOR COMPONENTLOCATION CHART

/

TERMINAL NUMBERA6 =

.5 BK

I

CHART ALSO SHOWSTOTAL NUMBER OFCONTACTS POSSIBLE:XZB I6 PIN)

A WAVY LINEWIRE INSULATION MEANS A WIREIS ONE COLOR

1 1.5 RO /IsTo nE

- ZZIYZJYATI~NIS ONE COLOR

5 ROiVL

WIRE SIZE IN MM ’

\5 ER

I !!!Y

T O T A C H O M E T E R ,PAGE 115/3

WITH ANOTHERCOLOR STRIPE(REO WITH YELLOW1

WIRE IS ATTACHED TOMETAL PART OF CARIGROUNOEO)

GROUND IS NUMBEREOFOR REFERENCE ONCOMPONENT LOCATION CHART

OTHER CIRCUITS THAT SHAREA G R O U N O A R E St(OWNI N G R O U N O OlSTRlBUTlON

CURRENT PATHIS CONTINUEDAS LABELEOTHE ARROW SHOWSDIRECTION OF CURRENTFLOW AN0 IS REPEATEDWHERE CURRENT PATHCONTINUES.

A WIRE WHICH CONNECTSTO ANOTHER CIRCUIT

R E V I S I O N S :

THIS FUSE FEEDS OTHESCIRCUITS WHICH ARE NOTS H O W N H E R E T H E S E CIRCUITSARE IDENTIFIED IN“POWER OISTRIBUTION”

me POWER OISTRIRUTION

GROUNOS b- CIRCUITS NOT SHOWN HERESHARE THIS CROUNO THESECIRCUITS ARE IOENTIFIEPIN” CROUNO DISTRIBUTION ”

r

x V A C U U M V A C U U M RESTRICTORS ARERESTRICTOR POROUS BRASS PLUGS

IN THE VACUUM HOSE.THE RESTRICTOR SLOWSTHE VACUUM FLOW

V E N T

A SWITCHOVER VALVE ISA SOlENOlO OPERATEDV A C U U M V A L V E T H EVALVE IS VENTEO WHENTHE COIL OF THESOLENOID IS OE ENERGIZED

VACUUM ELEMENTS PUSH ORPULL A SHAFT BETWEEN TWOFIXEO P O S I T I O N S W H E NVACUUM IS APPLIEO. THESHAFT IS PULLEO IN WHENNO VACUUM IS PRESENT,THE SHAFT IS PUSHEO OUTBY A SPRING

q TEMPERATURESENSOR

VACUUM CAN FLOWEASILV IN THE DIRECTIONOFTHEARROW. V A C U U MCANNOT FLOW AGAINSTTHE ARROW.

REVISIONS:

TROUBLESHOOTING

Determine the extent of the problem byoperating circuits which share the samefuse. If the other circuits work, the fuse isgood. The cause must be within the wiringunique to the problem circuit.

3. REFER TO THE E.T.M. AND ANA-LYZE THE CIRCUITStudy the circuit schematic to learn howthe circuit should operate. The schematicwill tell you:

D - Where the circuit receives current.F - What circuit protection is involved.

- What switches control current flow.- How the loads operate.Understanding the total circuit is neces-sary if you are to troubleshoot efficiently.Determine possible problem areas andtesting locations. The Component Loca-tion table tells where components andground points are located.

4. SYSTEMATICALLY TEST THE CIR-CUIT IN ORDER TO ISOLATE THEPROBLEM

TROUBLESHOOTING PROCEDURE

1. VERIFY THE COMPLAINTOperate the problem circuit in all modes tocheck the accuracy of the complaint. Thismay give a clue as to the extent, nature,and location of the problem.

2. CHECK THE FUSE AND RELATEDCIRCUITS

As a general guideline:- If the fault affects a single component of

a circuit, start to test at that compo-nent.

- If the fault affects a number of compo-nents of a circuit, start to test at thepoint where the circuit gets its power.

-5.

6.

MAKE THE REPAIRAfter you have narrowed the problemdown to a specific cause, repair as neces-sary.

A SERIES AMMETER must never be con-netted in parallel with a component. This cancause a short circuit and damage the meter.

VERIFY CIRCUITOPERATIONFirst operate the repaired circuit in allmodes to be sure you have fixed the entireproblem. Next, operate all circuits whichshare the same fuse. Be sure that this doesnot cause the problem to reappear.

TESTING TOOLSA VOLTMETER is used to measure voltage

at various points within a circuit. If an analogVOLTMETER is used, it must have aresistance of at least 20,000 ohms per volt inthe low range. Any digital VOLTMETERmay be used.

Use of an OHMMETER should be limitedto harness wiring, connections and switches.It should not be used on solid state compo-nents or relays. An OHMMETER measures acircuit for its resistance to current flow. Sincean OHMMETER has an internal battery thatprovides current to the circuit under test, it isfirst necessary to disconnect the car battery.This will ensure that there is no voltagealready present in the circuit.

An AMMETER measures the current flow-ing within a circuit. There are two types ofAMMETERS: the SERIES AMMETER andthe INDUCTIVE (clamp-on) AMMETER(e.g. Sun DMM-5). The INDUCTIVEAMMETER is clamped around a wire in thecircuit under test. The SERIES AMMETERmust be connected into the circuit.

REVISIONS:

T E S T S

Vokage Test

Connect the negative lead of the VOLT-METER to a known good ground or nega-tive (-) battery terminal.Connect the positive lead of the VOLT-METER to a point (connector or terminal)you wish to test.If the meter registers, there is voltage present. This voltage should be within onevolt of measured battery voltage. A loss ofmore than one volt indicates a problem. Aloose connection is a likely cause. Takereadings at several points along the circuitto isolate the problem.

BATTERYVOLTAGE,,---, l.liRD

0/

I

NO VOLTAGE

-\

3%J~E/RELAV‘ox

1 SOLENOID

Voltage Drop Test

This test checks for voltage being lost alonga wire, or through a connection or switch.

Connect the positive lead of the VOLT-METER to the end of the wire, or to theside of the connection which is closest tothe battery.Connect the negative lead to the other endof the wire, or the other side of the connec-tion.When the circuit is operated, the VOLT-METER will show the difference in voltagebetween the two points. A difference (ordrop) of more than one volt indicates aproblem.

Voltage Test Voltag

FlK~sEIRELAVBOX-

1 SOLENOIO

rop Test:e D:

Testing For Short to Ground With aVoltmeter

Remove the blown fuse and disconnect theload.Connect the VOLTMETER across the fuseterminals.Beginning near the fuse box, move the har-ness from side to side while watching theVOLTMETER.If the meter registers, there is a short toground in the wiring.

LOAD DISCONNECTELI

7-l SOLENOID

Testing for Short with Voltmeter

REVISIONS:

I 1 1 I I I I i i I i I i I I

Continuity Test

1. Check OHMMETER by adjusting the needle to zero while holding the leads together.

2. Disconnect the car battery.3. Connect one lead of the OHMMETER to

one end of the part of the circuit you wishto test.

4. Connect the other lead to the other end.5. If the meter shows low or no resistance,

there is continuity.

_OHMMETER

BAllERY DISCONNECTED

-!!

FlkE/AELAVBOX-

1.5 RO

_

4

1.5 no

• l

SOLENOIO. -

1.5 en

I‘=

TROUBLESHOOTINGTesting For Short to Ground With an Ohmmeter

1.

6.

Calibrate OHMMETER by adjusting theneedle to zero while holding the leadstogether.Remove the blown fuse and disconnect thebattery and load.Connect one lead of the OHMMETER tothe fuse terminal on the load side.Connect the other lead to a known goodground.Beginning near the fuse box, move the har-ness from side to side, while watching theOHMMETER.If there is no short, the meter will showinfinitely high resistance. If the meter registers low or no resistance, there is a shortto ground in the wiring.

BAITERY DISCONNECTED

OISCONWECTEO

Ql -

S0LEW0l0

1.5 BR

-. I=

Current Test With a Series Ammeter

1.

2.

3.

4.

Disconnect the circuit at a convenientpoint such as a connector.Connect a lead of the AMMETER to oneside of the open circuit.Connect the second lead of theAMMETER to the other side of the opencircuit. The AMMETER completes the cir-cuit.With the circuit operating, theAMMETER will show how much currentis flowing in the circuit.

FlFUSE~RELAVBOX-

Continuity Test Tenting for Short with Ohmmeter Current Test (Series Ammeter)

REVISIONS:

Current Test With an Inductive Ammeter1. Clamp the AMMETER pliers around the

wire under test in the circuit.2. With the circuit operating, the

AMMETER will show how much currentis flowing in the circuit.

2.5 BK

I N D U C T I V E 2.5 BK

2.5 BR

Current Test (Incjuctive Ammeter)

Troubleshooting Vacuum ComponentsA VACUUM TESTER is used to apply vac-

uum to vacuum components. The tester (M-Bpart no. 589 25 2100) registers in mbar of vac-uum. Two typical applications of this testerare shown below.

PERMISSIBLE LEAKS

Check Valves 5Ombarin 10min. et300 mbar vacuum

Other Vacuum 20 mbarlmin. atComponents 300 mbar vacuum

DISCONNECTEO

V A C U U MTESTER

ONCE VACUUM ISAPPLIEO, THE READINGSHOULO REMAINSTABLE WITHIN THELIMITSSHOWN ABOVE.

HOSEOISCONNECTEO

TESTER

V A C U U M ELEMENT SHAFT SHOULDE L E M E N T RETRACT AS VACUUM IS

APPLIED BY TESTER.ONCE VACUUM ISAPPLIED,THE READING SHOULDREMAIN STABLE WITHINTHE LIMITSSHOWN ABOVE.

Switchover Valves (as of MY 1984)The former switchover valves on all modelsare replaced by a standard switchover valve.

When de-energized (no current), the sideand the lower pipes are connected to eachother. When energized, the upper pipe con-nects to the side pipe. If only two pipes areused, a standard protective cap with vent isplugged onto the third pipe.

UPPER LOWERPlsE rlPE- -m-m-c3

SIDE iIPE

SCHEMATIC SYMBOL FOR SWITCHOVER VALVE

SWITCHOVER VALVE DE-ENERGIZE0

4

SWITCHOVER VALVE ENERGIZED

REVISIONS:

I I I I i i I I I i i I

CIRCUIT IDENTIFICATION

Circuit

1

Description

Negative side of ignition coil (lowvoltage).

4

15

15R

Output of ignition coil (high voltage).

Battery voltage; ignition/starter switch in“Run” (~0s. 2) of “Start”.

Battery voltage; ignition/starter switch in“Accy” (pos. 11, “Run” (pas. 21 or“Start”.

15Rl30

15x

Power feed for Power Seat Motors andTelescopic Steering Wheel.

Battery voltage; ignition/starter switch in“Run” (Pas. 2).

16

30

31

31b

49

49a

50

56

56a

Ignition switching unit connection fromnegative side of coil.

Battery voltage; “hot” at all times.

Ground.

56b

56d

580

Switched ground.

Turn signal/hazard flasher input.

Turn signal/hazard flasher output.

Starter motor control.

Power feed for headlamps.

Headlamps; high beam and indicatorlamp.

Headlamps; low beam.

Headlamp flasher.

Instrument lamp output; from ElectronicControl Unit.

58d Instrument lamp output; from Rheostat.

58L

5BR

58N

61

85

86

87

87a

K, K30

L

LA

N

NSE

P30

R

TD

Parking, tail, side marker lamps; left side.

Parking, tail, side marker lamps; right side.

Fog lamps.

Charge indicator.

Relay winding; ground side.

Relay winding; positive side.

Relay output; normally open.

Relay output; normally closed.

Battery voltage; exterior lamp switch in“Parking” or “Headlamp” position.

Turn signal lamps; left side.

Preglow indicator.‘

Fog lamp switch; output.

Fog lamp switch; input.

Battery voltage with exterior lamp switchin “Parking” or “Headlamp” position.

Power feed for R and L standing lamps;battery voltage with ignition/starterswitch in “Off” or “Accessory” position.

Turn signal lamps; right side.

Engine speed signal.

NOTE: Circuit identification numbers willappear on schematics inside componentboxes. Connector terminal numbers willappear on schematics outside componentboxes.

REVISIONS: