The second-generation Smart Fortwo (W451), made from 2008 to 2015, has fuse box diagrams available. These diagrams show where the fuse panels are located inside the car and explain which fuse controls what (fuse layout) and where relays are placed.
Table of Contents
Cigar lighter (power outlet) fuse in the Smart Fortwo is the fuse #21 in the Instrument panel fuse box.
Instrument Panel
| Fuse Number | Description | Fuse Amp |
|---|---|---|
| 1 | Engine 132.9, 660.9: Starter Engine 780.009: Brake booster vacuum pump | 25 |
| 2 | Wiper motor | 25 |
| 3 | Power window convenience feature control unit | 20 |
| 4 | Blower motor | 25 |
| 5 | Left front fog lamp Right front fog lamp | 10 |
| 6 | Right taillight Right parking lamp Left license plate lamp Right license plate lamp | 7.5 |
| 7 | Left taillight Left parking light | 7.5 |
| 8 | Engine 132.9: Secondary air injection pump relay ME-SFI [ME] control unit Electronic selector lever module control unit Automated manual transmission control unit Cylinder 1 ignition coil Cylinder 2 ignition coil Cylinder 3 ignition coil Engine 660.9: CDI control unit Electronic selector lever module control unit Automated manual transmission control unit Engine 780.009: High-voltage battery heater | 25 |
| 9 | Engine 132.9: O2 sensor downstream of CAT O2 sensor upstream of CAT Adjustable camshaft timing solenoid External air shutoff valve Activated charcoal canister shutoff valve EGR switchover valve (with engine 132.910) Tank vent valve Pressure regulator valve(for engine 132.930) Engine 780.009: Electric drive and high-voltage charger fan motor Engine 660.9: CDI control unit | 7.5 |
| 10 | Engine 132.9: O2 sensor upstream of CAT Secondary air injection pump switchover valve Cylinder 1 fuel injection valve Cylinder 2 fuel injection valve Cylinder 3 fuel injection valve Engine 780.009: Electric drive and high-voltage charger coolant pump Battery cooling system coolant pump Engine 660.9: Hot film mass air flow sensor O2-sensor upstream of CAT CDI control unit Glow output stage EGR switchover valve | 15 |
| 11 | ESP control unit | 25 |
| 12 | Instrument cluster Additional instruments Microwave sensor Rain sensor / light sensor Alarm siren with inclination sensor Left turn signal lamps/brake light relay Right turn signal lamps/brake light relay Mirror heater relay Automated manual transmission control unit TPM [RDK] control unit Combination switch Cockpit switch group Data link connector Starter-alternator control unit STH radio remote control receiver (engine 780.009) Rear fog light relay | 10 |
| 13 | Spare fuse | 15 |
| 14 | Refrigerant compressor Charge air fan motor | 15 |
| 15 | Smart radio 9 Smart radio 10 Front interior lamp Soft top OPEN relay Soft top CLOSE relay | 15 |
| 16 | Engine 132.9: Fuel pump with fuel gauge sensor ME-SFI [ME] control unit Engine 660.9: Fuel pump with fuel gauge sensor CDI control unit Engine 780.009: Blower motor relay 1 | 15 |
| 17 | Rear-end door wiper motor | 15 |
| 18 | Instrument cluster Yaw rate sensor for lateral and longitudinal acceleration Seat occupied recognition pressure sensor Automatic child seat recognition airbag OFF indicator lamp Restraint systems control unit ESP control unit Steering angle sensor Steering assist control unit Driver side seat belt buckle restraint systems switch Front passenger-side seat belt buckle restraint systems switch | 10 |
| 19 | Engine 132.9: ME-SFI [ME] control unit Automated manual transmission control unit Data link connector TPM [RDK] control unit Starter-alternator control unit Engine 780.009: Data link connector Engine 660.9: CDI control unit Automated manual transmission control unit Data link connector | 7.5 |
| 20 | Smart radio 9 Smart radio 10 Heater/air conditioning operating unit Front seat heater (SIH) control unit Right wiper switch Outside mirror adjustment switch Electrically adjustable and heated outside mirrors Soft top operation Electronic selector lever module control unit | 10 |
| 21 | Interior socket | 15 |
| 22 | Left low beam | 7.5 |
| 23 | Right low beam | 7.5 |
| 24 | Engine 132.9: Electronic selector lever module control unit Engine 132.9, 660.9, 780.009: Rear fog light relay Stop light switch | 15 |
| 25 | Right high beam | 7.5 |
| 26 | Left high beam | 7.5 |
| 27 | Engine 132.9: ME-SFI [ME] control unit | 7.5 |
| 28 | Heated rear window | 40 |
| 29 | Soft top OPEN relay Soft top CLOSE relay | 30 |
| 30 | Engine 132.9, 660.9: Automated manual transmission control unit Engine 780.009: High-voltage battery and interior fan motor | 40 |
| 31 | Horn Right door CL motor Left front door central locking motor Rear-end door CL [ZV] motor Fuel filler flap CL [ZV] motor Horn switch | 20 |
| 32 | Vacant | – |
| 33 | Ignition/starter switch | 50 |
| 34 | ESP control unit | 40 |
| 35 | Steering assist control unit | 30 |
| R1 | Engine 132.9, 660.9: Mirror heater relay | 7.5 |
| R2 | Engine 132.9: Stop light switch | 7.5 |
| R3 | Vacant | – |
| R4 | Engine 780.009: Mirror heater relay | 7.5 |
| R5 | Engine 780.009: High-voltage charger control unit External socket communications control unit | 7.5 |
| R6 | Engine 780.009: EVCM electric vehicle control unit | 15 |
| R6 | Engine 132.9, 660.9: Backup lamp relay Brake light relay | 10 |
| R7 | as of 2.9.10; engine 132.9: Front interior lamp Engine 660.9: Front interior lamp | – |
| R7 | Engine 780.009: EDCM electric motor control unit | 10 |
| R8 | as of 2.9.10; engine 132.9: Sound system amplifier Engine 660.9: Sound system amplifier | 20 |
| R8 | Engine 780.009: PDU high-voltage distributor control unit | 7.5 |
| R9 | Engine 132.9, 660.9: Front seat heater (SIH) control unit Engine 780.009: Brake booster vacuum pump control unit | 25 |
Fuses near the battery
| Fuse Number | Description | Fuse Amp |
|---|---|---|
| F36 | Engine 132.9: Secondary air injection pump | 50 |
| F58 | Engine 780.009: EDCM electric motor control unit | 60 |
| F58 | Engine 132.9: Starter Alternator | 200 |
| F91 | SAM control unit | 100 |
Relays
| Relay Number | Relays |
|---|---|
| A | Left turn signal/stop lamp relay High-voltage battery heater booster relay (only ECE vehicles) |
| B | Right turn signal/stop lamp relay Radiator fan motor relay (only ECE vehicles) Fuel pump relay |
| C | Mirror heater relay Rear fog light relay |
| K57 | High-voltage battery heater booster relay |
| K59 | Radiator fan motor relay |
| K61 | Blower motor relay 1 |
| K62 | Blower motor relay 2 |
Also Read: What is car fuse box diagram? Important to know.
Frequently Asked Questions (FAQs)
My 12V power socket (cigarette lighter) is not working. Which fuse should I check?
This is a top source of fuse failure due to overloading.
Fuse Location: Check the Driver’s Side SAM Unit / Fuse Box.
Fuse Type: Look for a fuse labeled “Accessory Socket,” “Cigar Lighter,” or “12V.” It is typically a 15 Amp (Light Blue) or 20 Amp (Yellow) fuse.
The windshield wipers, washer pump, or horn suddenly stopped working. Which fuses protect them?
These exterior components are fused within the main panel.
Wiper Motor: Check the fuse labeled “Wiper Motor” (often a 30 Amp Green fuse).
Horn/Washer Pump: Check the fuses labeled “Horn” and “Washer Pump” (typically 10 Amp or 15 Amp fuses).
My radio, stereo, or interior lights have failed. Which fuse should I check?
These systems are protected by low-amperage fuses in the main fuse box.
Radio/Audio: Check the fuse labeled “Audio” or “Radio” (often 10 Amp Red).
Interior/Room Lights: Check the fuse labeled “ROOM” or “Interior Lamp” (typically 5 Amp or 10 Amp).
My engine is overheating, and the cooling fan is not turning on. Where is the fuse for the fan?
Due to the rear engine, the cooling fan is critical. Its fuse and relay are integrated into the main SAM unit.
Location: Check the large fuses and associated relays within the SAM Unit / Fuse Box labeled “Cooling Fan” or “Radiator Fan.” If this high-amperage fuse is blown, the fan motor or its wiring has likely failed, causing the overload.
I have multiple, unrelated electrical failures (e.g., headlights, central locking, and stereo all failed). Could this be a fuse?
The SAM unit is known to be vulnerable to moisture ingress or internal corrosion. If you find all your fuses are intact but many systems are dead, the SAM unit may require professional diagnosis or replacement, as it acts as the primary electrical junction box.