Mercedes-Benz 203 fuse and relay

Mercedes 203 C-class represents the second generation of the model range which was produced in 2000, 2001, 2002, 2003, 2004, 2005, 2006 and 2007 with w203 sedan, s203 station wagon, coupe (C160, C180, C230, C240, C280, C320). During this time, the model has been restyled. In this publication you will find information on the location of electronic control units, a detailed description of the fuses and relays Mercedes 203 with box diagrams and photo examples of their location. Note the fuses responsible for the cigarette lighter and fuel pump.


The location of the blocks and the design of the elements in them may differ from the one shown and depends on the year of manufacture, the region of delivery and the level of electrical equipment of your car.





1Air conditioner/heater control unit – in the heater control panel
2A/C/Heater Fan Control Module – Next to the fan motor
3Air purity sensor (air conditioning system)
4Sunlight sensor (air conditioning system)
5Antenna signal booster – 1, rear window top
7Anti-theft control unit (integrated with the multifunctional control unit) – left side of the luggage compartment
8Vehicle inclination sensor (anti-theft system) – left side of the luggage compartment
9Anti-theft horn – Behind wheel arch trim
10Volume change sensors (anti-theft system)
11Audio unit – in navigation system
12Audio output amplifier (if equipped) – right side of luggage compartment
13Additional heater control unit
14Auxiliary Heater Remote Control Receiver – Under Dashboard (Rear Luggage Compartment)
15Accumulator battery
16Brake booster vacuum pump control unit
17Central locking signal sensor (infrared) – in the handle of the driver’s door
18Diagnostic connector (DLC)
19Driver’s door electrical control unit
20Left rear door electrical control unit
21Passenger door electrical control unit
22Control unit for electrical equipment of the right rear door
23Fuse/Relay Box, Engine Compartment 1
24Fuse box/relay dashboard
25Fuse/Relay Box, Luggage Compartment
26Headlight control unit, left (models with xenon headlights)
27Headlight control unit, right (models with xenon headlights)
28Sound signals 1/2 – behind the grille
29Ignition lock control unit
30Electronic immobilizer control unit – (integrated with ignition lock control unit)
31Turn signal/alarm relay – in multifunction control box 2
32Lighting control unit – behind the headlight switch
34Multifunction Control Module 1 – Attached to Engine Compartment Fuse/Relay Box – Functions: Interior Lamps, Headlights, Horns, Windshield Wipers, A/C Pressure Control, Headlight Washers, Coolant Level, Brake Fluid Level, Thermometer, Power Actuator door mirrors
35Multifunction control unit 2 – connected by fuse / relay box, luggage compartment – functions: Central locking, fuel level, anti-theft system, alarm, rear window defroster, taillights, trunk lid opener, rear window wiper (wagon)
36Navigation system control unit
37Ambient temperature sensor
38Parking system control unit – under the panel, in the rear of the luggage compartment
39Rain sensor – upper center windshield
40Power seat control unit (with memory), front left – under the seat
41Power seat control unit (with memory), front right – under the seat
42Seat heating control unit, front – in the switch block
43Electronic transmission control unit – sequential manual transmission
44Side impact sensor, left – under the rear seat
45Side impact sensor, right – under the rear seat
46SRS electronic control unit
47Steering column electrical control unit – behind the steering wheel
48Steering column lock control unit – built into the ignition lock control unit
49Sunroof electric control unit
50Body height sensor, front (models with xenon headlights) – front anti-roll bar
51Body height sensor, rear (models with xenon headlights) – rear axle
52Telephone network connection module – under the panel, in the rear of the luggage compartment
53Telephone interface control unit – under the panel, in the rear of the luggage compartment
54Phone transceiver – under the panel, in the rear of the luggage compartment
55Trailer electrical control unit – under the panel, in the rear of the luggage compartment
56Electronic gearbox control unit
57Shift control unit – automatic transmission selector
59Voice activation system unit – under the panel, in the rear of the luggage compartment
60Fuse/Relay Box, Engine Compartment 2

The location of the fuse and relay boxes in the Mercedes w203



  • F32 – Power fuse box
  • F34 – Fuse box in the instrument panel
  • N10/1 – Fuse and relay box in the engine compartment
  • N10/2 – Fuse box and relay luggage compartment

Passenger compartment

In the cabin, the fuse box is located on the left side of the dashboard behind a protective cover.





2130A Left front door control unit
2230A Right front door control unit
2315A Cigarette lighter
247.5A CD player with changer (in glove compartment)
2530A Upper control panel control unit
2625A Audio Amplifier
2730A Driver’s seat power adjustment control unit (with memory)
2830A Spare fuse
2930A Driver’s seat power adjustment control unit (with memory)
Multifunctional control unit (taxi)
3040A Heater air circulation unit
3120A EIS control unit
Ignition lock control unit
3230A Left rear door control unit
3330A Right rear door control unit
347.5A Terminal 30 socket
Until 31.5.01:
Cell phone and D2B transceiver (for built-in phone)
Cell phone and transceiver TELE AID D2B (for built-in phone)
Phone interface (for optional cell phone)
CTEL compensator (for additional cell phone)
15A Before 31.3.04: Power passenger seat adjustment control unit (with memory)
Until 31.5.03, Taxi: Multifunctional control unit
From 1.6.03, Taxi: Multifunction control unit
From 1.6.01, Police: Multifunction control unit
30A From 1.4.04: Passenger seat power adjustment control unit (with memory)
From 1.4.04, Taxi: Multifunction control unit
3530A Until 31.3.04: STH heater unit
20A From 1.4.04: STH heater unit
3630A Before 31.3.04, Police: Additional equipment power connector
15A Engines 612.990 (up to 29.2.04): Charge air cooler circulation pump
From 1.4.04, Japan: Audio interface control unit
7.5A Universal mobile phone interface
3725A Air cooler circulation pump
Up to 29.2.04: Brake booster vacuum pump control unit
3830A Up to 29.2.04: Power passenger seat adjustment control unit (with memory)
From 1.4.04, Police: Multifunction control unit
3930A Spare fuse
407.5A Passenger seat power adjustment control unit (with memory)
Universal mobile phone interface
cell phone separation point
Telephone interface
Radiotelephone network compensator E
From 1.6.01, MB phone: Cell phone and transceiver
From 1.6.01, TELE AID: Cell phone and transceiver
From 1.4.04, Japan: E-call control unit
30A Up to 31.5.01: Multifunction control unit
417.5A Upper control panel control unit
Up to 31.5.01: KLA system control panel (Automatic climate control system)
15A From 1.6.01: KLA system control panel (Automatic climate control system)
427.5A Instrument cluster

In the Mercedes 203, fuse 23 is responsible for the cigarette lighter. Another fuse is located in the block under the hood or luggage compartment (USA).

Engine compartment

Main fuse and relay box

Under the hood in the engine compartment on the left side under the protective cover is the fuse and relay box (N10/1).

photo 1


Diagram 1


43a15A Horn relay
43b15A Horn relay
445A D2B interface
Telephone interface
Connector ferrule 15R
TELE AID control unit
457.5A SRS control unit
4640A Wiper On/Off Relay
Wiper Mode Relay 1/2
4715A Glove box lights with sensor-switch
Front cigarette lighter (illuminated)
4815A Engines 612.990 (up to 31.3.04): Brake booster vacuum pump control unit
Motors 112, 113: Fuse-protected connector sleeve 15
Engines 646, USA (up to 31.3.04): Fused connector sleeve 30
Engines 646 (from 1.4.04): O2 probe before catalytic converter
497.5A SRS control unit
505A Light switch module
Engines 612.990
Preheating output stage (until 31.3.04)
Mass Air Flow Sensor (1.4.04 to 30.11.04)
517.5A AAC (automatic A/C) with built-in auxiliary fan electric motor
instrument cluster
For AAS “comfort”:
AAC failure sensor
Solar radiation sensor AAC (4 pieces)
For all vehicles with xenon headlights:
Left block headlight
Right block headlight
AMG: Charge air cooler circulation pump
203.0 (until 31.7.01): SRS control unit
5215A Starter
5325A Diesel engines:
Starter relay
Rear SAM control box with relay and fuse box
Engines 611/612/642/646: CDI control unit
15A Gasoline engines:
Starter relay
Rear SAM control box with relay and fuse box
Engines 111/271/272: ME control unit
Engines 112/113:
ME control unit
Cable termination electr. circuit terminal 87 M1e
5415A Engines 271.940:
ME control unit
Vent valve (USA)
Canister shut-off valve
Engines 271.942: NOX control unit
Engines 642/646: CDI control unit
Motors 642/646: Cable termination electr. terminal 30 circuits
7.5A Engines 611/612: CDI control unit
Engines 611/612 (until 11/30/04): Heating element in the ventilation duct
557.5A Steering wheel sensor
Distronic: DTR control unit
Gearbox 722:
ETC control unit [EGS] (up to 31.5.04)
Selector lever electronic control unit
VGS control unit
Gearbox 716:
Sequentronic control unit
Transmission Position Sensor
565A ESP and BAS control unit
Brake light switch
575A Steering wheel sensor (up to 31.5.02)
Electronic ignition control unit / sensor-switch opening the starter circuit
Steering column electronic module (as of 1.6.02)
Engines 112/113: ME control unit
5840A Transmission 716: Hydraulic pump
5950A ESP and BAS control unit
6040A ESP and BAS control unit
6115A Transmission 716: Sequentronic control unit
625A Diagnostic connector
Lighting control module
Brake light switch
635A Lighting control module
6410A Radio receiver
Radio and navigation
Display and function control unit COMAND
6540A Engines 112/113: Electric air pump
IHorn relay
KTerminal 87 relay, chassis
LWiper Mode Relay 1/2
MRelay terminal 15R
NKSG pump control relay
OAir Pump Relay (Engines 112, 113, 271)
PRelay terminal 15
QRelay on/off wiper
RTerminal 87 relay, motor
SStarter relay

Power fuse box

An additional high power fuse box in the form of fuse links is installed next to the battery.


Photo example

photo 5




  1. 125A Fuse box in the instrument panel
  2. 200A SAM control unit, rear
  3. 125A Additional fuse box
  4. 200A SAM control unit, front
  5. 125A Electric suction fan for engine and air conditioner with integrated regulator Diesel engines: Preheat output stage
  6. 60A SAM control unit, front

Luggage compartment

It is located in the luggage compartment behind the trim.

lug component




130A Front right seat adjustment switch box
Switch for partially electric adjustment of the front passenger seat
230A Front left seat adjustment switch box
Driver’s seat partially electric adjustment switch
37.5A Interior lighting
trunk lighting
Remote control receiver
Tire inflation pressure control
20A TV tuner
420A Fuel pump relay
520A Engines 112.961 (up to 31.3.04): Charge air cooler circulation pump
Except 112.961: Reserve relay 2
625A Spare fuse
77.5A Backup relay 1
87.5A Rear window aerial amplifier module
Alarm siren
ATA tilt sensor
925A Overhead control panel control box
1040A Rear window defroster
1120A Spare fuse
1215A Accessory Power Connector
203.0 – USA (until 31.3.04): Rosette
135A Air pump for multi-contour seat
Voice Control System (VCS) – Voice Control Unit
Cell phone Motorola Star TAC, retrofit – D2B interface for portable mobile phone
Rear Reading Light
Signal display PTS (Parktronic)
PTS control unit (parktronic)
1415A Rear stack wiper
1510A Filler relay, polarity receiver
1620A For VSC: Voice control box
For CTEL Motorola Star TAC, retrofit: D2B interface for mobile phone
1720A Trailer control unit
1820A Drawbar socket, 13-pin
1920A Air pump for multi-contour seat
2015A Rear window dimming
203.2/7 – USA: Rosette
AFuel pump relay
BRelay 2, terminal 15R
CBackup relay 2
DBackup relay 1
ERear defroster relay
FRelay 1, terminal 15R
GFiller relay, polarity switch 1
HFiller relay, polarity switch 2


There is something to supplement this post – write in the comments.

Comments 7

  • have a 2006 c230 MBZ Instrument Cluster will not go a sleep at night – odomoter window
    stays illuminated and drains battery…tried changing the cluster to a used one….it worked
    did the reset with all….Light went off….all good….then in the evening …the light appeared again (the odometer box only-the 2 boxes in the middle of cluster ??) so it did it again- Is there a relay for the Accessory delay RELAY? a speedo guy said to change that out ?

  • back up relay 2 an 1, or C an D, what are they used for

  • I have a mercedes C220 2006
    My expartner removed the starter relay (con trick for blackmail).
    Not knowing I tried to tow it to a safer place it was left on a school crossing.

    I tried to un lock with fob new batteries by main dealer.

    No response head lights on ,radiator fan on all the time. It’s a crying shame. Iv got NO WORKING KIDNEYS HAEMODIALYSIS PATIENT LITTLE MONEY

  • that’s very helpful

  • Fiited a new engin Sam box, in mercedes c180 2002, car still doesn’t want to start need help to diagnose the problem starter swing perfectly when by passed from battery direct to starter.

  • My c220 2003 parking lights do not turn off after locking the car please any help

  • The M position in the front SAM panel is labeled as M15 and is a relay. The wired connector is plugged in from the top and has 5 wires going to it. They are as follows, grey wire w/purple stripe, brown w/yellow stripe, red w/stripe, blue w/red stripe, and a heavier gauged wire that is red w/yellow stripe. The red yellow wire is in the loom but splits off and goes downward in front of the SAM box but can’t seem to see where it goes yet. The other four comes out of the box and heads towards the front of the car with the wires dangling not conectes to anything. I don’t see any other place where it may have come from. I’ve done extensive research online but I guess I’m not looking in the right places. This is the first chat room that even came close to what I was talking about. If anyone is familiar with anything mentioned here please share anything that might help me get to the next level of figuring this out. Thanks!

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