Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1990 Mercedes Benz 350SDFACTORY OEM SERVICE PROCEDURE
Control Units
CONTROL UNITS LOCATION
| Component Name, Number | Location |
|---|---|
| ABS Control Unit, N30 | Center rear of engine compartment, mounted to firewall. See Figure . |
| ABS/ASR Control Unit, N30/1 | Center rear of engine compartment, mounted to firewall. See Figure . |
| A/C Compressor Control Unit | Right rear of engine compartment, behind battery. |
| A/C Temperature Control Unit | Under right side of dash, behind glove box. |
| Amplifier Speaker Control Unit, N40/1 | In luggage compartment, behind front trim panel. See Figure . |
| Anti-Theft Alarm Control Unit | Under right side of passenger foot rest, near kick panel. |
| ASD Control Unit, N47 | Left rear corner of engine compartment, attached to engine heat shield. See Figure . |
| Automatic Climate Control Unit, N22 | In center console. See Figure . |
| Auxiliary Heater Control Unit, N33 | Centered, under passenger-side foot rest. See Figure . |
| Control Unit Comfort Seat Adjustment (Left), N31 | Under left front seat. See Figure . |
| Control Unit Comfort Seat Adjustment (Left With Memory), N31/1 | Under left front seat. See Figure . |
| Control Unit Comfort Seat Adjustment (Right), N32 | Under right front seat. See Figure . |
| Control Unit Comfort Seat Adjustment (Right With Memory), N32/2 | Under right front seat. See Figure . |
| Control Unit Compressor Cut-Out, N6 | Left rear corner of engine compartment, attached to engine heat shield. See Figure . |
| Control Unit Electronic Accelerator, N4/1 | Under dash left of steering column. See Figure . |
| Convenience Control Unit | Under left side of rear seat. |
| Cruise Control Amplifier With Reference Resistor, N4/2 | Under dash, left of steering column. See Figure . |
| Cruise Control Unit, N4 | Under dash, left of steering column. See Figure . |
| Daytime Running Light (DRL) Control Unit | Centered, under right side foot rest. |
| EDS Control Unit, N39 | Right rear of engine compartment, behind battery. See Figure . |
| EDW Control Unit, N26 | Centered, under passenger-side foot rest. See Figure . |
| Electronic Blower Regulator Control Unit | Center of cowl, next to heater core. |
| Exterior Light Failure Monitoring Unit | Left rear corner of engine compartment, in fuse/relay box. |
| Engine Systems Control Unit (MAS) | Right rear of engine compartment, behind battery. |
| Emergency Tensioning Retractor (ETR) Control Unit, N2/1 | Top of transmission tunnel, behind front console. See Figure . |
| Front Seat Heater Control Unit, N25/5 | Under respective seats. See Figure . |
| Hydropneumatic Suspension Control Unit, N46 | Under dash left of steering column. See Figure . |
| Idle Speed Control Unit, N8 | Centered, under passenger-side foot rest. See Figure . |
| Illumination Control Unit | On steering column, behind instrument cluster. |
| Left Front Power Seat & Steering Column Adjustment Control Unit, N32/3 | Under left front seat. See Figure . |
| Left Seat Belt Extender Control Unit, N42 | In luggage compartment, Behind front trim panel. See Figure . |
| Rear Seat Heater Control Unit, N25/6 | In luggage compartment, under front trim panel. See Figure . |
| Right Seat Belt Extender Control Unit, N43 | In luggage compartment, behind front trim panel. See Figure . |
| SRS Control Unit, N2/2 | Top of transmission tunnel, behind front console. See Figure . |
| Tempmatic Control Unit, N20 | Under passenger-side of dash, behind glove box. See Figure . |
| Trailer Monitoring Control Unit, N28/1 | In luggage compartment, under trim panel. See Figure . |
| Trip Computer Control Unit, N41 | Behind instrument cluster. See Figure . |
| Warning Module (Seat Belts), N2/4 | Behind instrument cluster, on steering column. See Figure . |
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.