Mercedes-Benz C-Class W203, S203 and CL203 (2000-2007) use rear, dashboard and engine-compartment fuse modules. The precise circuits depend on engine, body type, options, market and build date. This article keeps all known variations and spare positions instead of applying one rating to every vehicle.
Numbering runs across the modules: F1-F20 at the rear SAM, F21-F42 at the dashboard end panel and F43-F65 in the front SAM. The additional high-current distribution block is numbered independently. Do not follow generic charts that restart all three primary modules at fuse 1.
Where are the fuse boxes in a Mercedes W203?
Luggage compartment: switch off the ignition, open the boot or tailgate, and remove or fold back the appropriate side lining. The rear SAM is behind the trim. Its exact access panel differs between saloon W203, estate S203 and SportCoupe CL203.
Dashboard: open the driver’s door, remove the cover at the end of the dashboard and locate the F21-F42 panel. Read the chart on the cover or the fuse assignment card before replacement.
Engine bay: open the bonnet with the ignition off. The front SAM is on the left-hand side of the engine compartment under a protective cover. It supplies positions F43-F65 and the front relay group. High-current pre-fuses are housed separately in the main electrical distribution system.
The older W202 and newer W204 C-Class do not share this fuse assignment. Other guides are available under Mercedes-Benz fuse box diagrams.
Common Mercedes W203 fuses at a glance
These quick-reference circuits are also included in the complete tables below. Ratings separated by a slash represent installation alternatives.
| Pozycja | Amperaż [A] | Chroniony obwód / funkcja |
|---|---|---|
| F47 | 15 | Front cigarette lighter and glovebox light |
| F12 | 15 | Rear / additional 12 V outlet (body style and market dependent) |
| F4/A | 20 | Petrol fuel pump, controlled by rear SAM relay A |
| F46 | 40 | Front windscreen wiper motor |
| F14 | 10 / 15 | Rear wiper on applicable body styles |
| F10 | 40 | Heated rear window |
| F64 | 10 | Radio / COMAND |
| F62 | 5 | OBD diagnostic connector |
| F43 | 15 | Horn, circuits via relay I |
Rear SAM – luggage compartment fuses F1-F20
The rear SAM protects seat adjustment, the petrol fuel pump, rear-window heating, 12 V outlets, alarms and some trailer and comfort equipment. Equipment-dependent slots remain in this list.
| Pozycja | Amperaż [A] | Chroniony obwód / funkcja |
|---|---|---|
| 1 | 30 | Front passenger seat adjustment / memory |
| 2 | 30 | Driver seat adjustment / memory |
| 3 | 7,5 / 20 | Interior and luggage lighting, parking heater receiver or TV tuner, depending on equipment and production date |
| 4 | 20 | Petrol fuel pump via relay A |
| 5 | 20 | M112.961 through March 2004: charge-air cooling pump; otherwise spare circuit |
| 6 | 25 | Reserved circuit |
| 7 | 7,5 | Reserved circuit / spare relay |
| 8 | 7,5 | Antenna amplifier, alarm siren and tilt / anti-tow sensor |
| 9 | 25 | Overhead control panel / roof electronics |
| 10 | 40 | Rear-window heating |
| 11 | 20 | Reserved circuit |
| 12 | 15 | 12 V outlet / rear power socket according to body style and market |
| 13 | 5 | Multicontour-seat pump, voice control, phone, rear lighting and PARKTRONIC depending on equipment |
| 14 | 10 / 15 | Rear-window wiper on applicable body styles; equipment-dependent rating |
| 15 | 10 | Fuel filler flap actuator and reversing-polarity relay circuit |
| 16 | 20 | Voice control / phone |
| 17 | 20 | Trailer detection controller |
| 18 | 20 | Trailer electrical socket |
| 19 | 20 | Pneumatic pump for multicontour seats |
| 20 | 7,5 / 15 | Rear sunblind or additional outlet, depending on body style and equipment |
Rear SAM relay sockets A-H
Relay locations are shown separately from blade fuses, including both spare positions.
| Pozycja | Amperaż [A] | Chroniony obwód / funkcja |
|---|---|---|
| A | Przekaźnik pompy paliwa. | Fuel pump relay |
| B | Przekaźnik zacisku 15R nr 2. | Terminal 15R relay no. 2 |
| C | Przekaźnik rezerwowy nr 2. | Spare relay no. 2 |
| D | Przekaźnik rezerwowy nr 1. | Spare relay no. 1 |
| E | Przekaźnik ogrzewania tylnej szyby. | Heated rear window relay |
| F | Przekaźnik zacisku 15R nr 1. | Terminal 15R relay no. 1 |
| G | Przekaźnik zmiany polaryzacji klapki wlewu paliwa 1. | Fuel filler flap polarity-reversal relay no. 1 |
| H | Przekaźnik zmiany polaryzacji klapki wlewu paliwa 2. | Fuel filler flap polarity-reversal relay no. 2 |
Petrol fuel pump not running: check rear SAM F4 (20 A) together with relay A, then test the pump supply and circuit. For failed rear-window demisting, start with F10 (40 A) and relay E. Depending on body style, F12 (15 A) protects a rear auxiliary socket.
Dashboard fuse panel F21-F42
This panel serves door electronics, seat modules, the heater fan, EIS/EZS ignition and steering lock, telephone and special-purpose equipment. The functions of F34-F40 changed during production.
| Pozycja | Amperaż [A] | Chroniony obwód / funkcja |
|---|---|---|
| 21 | 30 | Left front door control module |
| 22 | 30 | Right front door control module |
| 23 | 15 | Through 30 November 2004: central gateway / variant-dependent circuit |
| 24 | 7,5 | Glovebox CD changer, where fitted |
| 25 | 30 | Overhead control panel |
| 26 | 25 | Audio amplifier |
| 27 | 30 | Driver seat memory controller / special-purpose vehicle controller |
| 28 | 30 | Reserved circuit |
| 29 | 30 | Driver seat controller / special-purpose vehicle functions |
| 30 | 40 | Heating and air-conditioning blower |
| 31 | 20 | Electronic ignition switch EIS/EZS and electric steering lock |
| 32 | 30 | Left rear door control module |
| 33 | 30 | Right rear door control module |
| 34 | 7,5 / 15 / 30 | Telephone / TELE AID / passenger seat / special equipment – production date and market dependent |
| 35 | 20 / 30 | Auxiliary parking heater STH – production date dependent |
| 36 | 7,5 / 15 / 30 | Interior power socket / audio gateway / UHI / police equipment – variant and date dependent |
| 37 | 25 | Charge-air cooling pump / brake booster vacuum pump on relevant engines |
| 38 | 30 | Passenger seat memory / special-purpose vehicle controller – date dependent |
| 39 | 30 | Reserved circuit |
| 40 | 7,5 / 30 | Passenger seat / telephone / TELE AID / special equipment – model year dependent |
| 41 | 7,5 / 15 | HEAT/AAC climate control unit – rating depends on production date |
| 42 | 7,5 | Instrument cluster |
No cabin ventilation: F30 is the listed 40 A heater blower supply; if intact, test the motor and speed controller. For window faults check the corresponding door control module, then the flexible wiring loom between the door and body.
Front SAM – engine bay fuses F43-F65
The front SAM provides the front cigarette lighter, wiper, horn, starter, SRS, engine management, radio / COMAND and ESP/BAS circuits. In particular, CDI and ME-SFI engines have different possible F53 and F54 ratings.
| Pozycja | Amperaż [A] | Chroniony obwód / funkcja |
|---|---|---|
| 43a | 15 | Horn via relay I |
| 43b | 15 | Horn via relay I |
| 44 | 5 | Telephone / TELE AID / phone interface |
| 45 | 7,5 | SRS airbag controller |
| 46 | 40 | Front wiper motor, operating and speed relays |
| 47 | 15 | Front cigarette lighter and glovebox illumination |
| 48 | 15 | Brake booster vacuum pump / engine systems depending on engine and date |
| 49 | 7,5 | SRS controller |
| 50 | 5 | Lighting control module or engine controls on selected diesels |
| 51 | 7,5 | Air conditioning, instruments, headlamp levelling and fan depending on equipment |
| 52 | 15 | Starter motor |
| 53 | 15 / 25 | Engine controller and rear SAM; CDI diesel can use 25 A, ME-SFI petrol 15 A |
| 54 | 7,5 / 15 | CDI or ME-SFI controller and engine circuits depending on engine |
| 55 | 7,5 | Steering angle sensor, DISTRONIC, transmission / Sequentronic according to equipment |
| 56 | 5 | ESP/BAS and brake light switch |
| 57 | 5 | Steering angle sensor, EIS/EZS, steering column module and ME-SFI on selected engines |
| 58 | 40 | Sequentronic hydraulic pump |
| 59 | 50 | ESP/BAS controller |
| 60 | 40 | ESP/BAS controller |
| 61 | 15 | Sequentronic transmission controller |
| 62 | 5 | OBD/DLC diagnostic socket, lighting module and brake-light switch |
| 63 | 5 | Lighting control module |
| 64 | 10 | Radio / navigation radio / COMAND |
| 65 | 40 | M112/M113 secondary air injection pump |
Front SAM relays I-S
| Pozycja | Amperaż [A] | Chroniony obwód / funkcja |
|---|---|---|
| I | Przekaźnik klaksonu. | Horn relay |
| K | Przekaźnik obwodu 87 podwozia / zależnie od wariantu układu. | Chassis circuit 87 relay, variant dependent |
| L | Przekaźnik prędkości 1 i 2 wycieraczek. | Wiper speed 1 / speed 2 relay |
| M | Przekaźnik zacisku 15R. | Terminal 15R relay |
| N | Sequentronic: przekaźnik pompy hydraulicznej. | Sequentronic hydraulic pump relay |
| O | Przekaźnik pompy wtórnego wtrysku powietrza – M112/M113/M271. | Secondary-air injection pump relay (M112/M113/M271) |
| P | Przekaźnik zacisku 15. | Terminal 15 relay |
| Q | Przekaźnik włącz/wyłącz wycieraczek. | Wiper on/off relay |
| R | Przekaźnik obwodu 87 silnika. | Engine circuit 87 relay |
| S | Przekaźnik rozrusznika. | Starter relay |
The front cigarette lighter uses F47 (15 A) in the documented layout. The front wiper circuit is F46 (40 A), the radio / COMAND F64 (10 A), and the OBD connector F62 (5 A). Check which option and engine configuration is installed before replacing F53 or F54.
Main high-current pre-fuse block
The main fuse block feeds entire fuse modules and higher-load electrical consumers. These 60-200 A links must be serviced using the correct battery isolation procedure rather than handled like ordinary blade fuses.
| Pozycja | Amperaż [A] | Chroniony obwód / funkcja |
|---|---|---|
| 1 | 125 | Dashboard fuse panel feed |
| 2 | 200 | Rear SAM / luggage compartment fuse box supply |
| 3 | 125 | Additional fuse carrier / distribution block |
| 4 | 200 | Front SAM / engine compartment fuse box supply |
| 5 | 125 | Engine and air-conditioning fan, or glow plug control unit on diesels |
| 6 | 60 | Additional front SAM / engine bay fuse box feed |
Fault checks and production-year differences
Horn inoperative: check the two front SAM horn circuits F43a and F43b (15 A each) and relay I. Multiple unrelated systems without power: the common supply, pre-fuse or SAM grounding may require investigation.
Repeatedly blown fuse: trace the short circuit or overloaded component and never increase the fuse rating. Uncertain year / engine assignment: consult the actual vehicle’s original fuse card. The W203 series received several electrical revisions, and options such as Sequentronic, TELE AID, multicontour seats and parking heaters are not fitted to every vehicle.