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.
DME/MOTRONIC Control Unit: Notes
A 55-pin DME/Motronic control unit is used in 535i, 735i and 735iL. An 88-pin control unit is used on all other models. See DME/MOTRONIC CONTROL UNIT LOCATION table. The control unit uses input signals from the following engine sensors to determine optimum fuel injection and ignition timing: intake airflow, intake air temperature, throttle position, coolant temperature, engine speed, vehicle speed, crankshaft position and exhaust gas oxygen content.
The DME/Motronic control unit can operate engine in a "limp mode," allowing vehicle operation despite component failure. The DME/Motronic control unit also has adaptive capabilities to compensate for component wear and other factors, such as minor air (vacuum) leaks. Once a fault is recognized, it is stored in DME/Motronic control unit memory as a fault code. The system automatically substitutes a fixed replacement value for the incorrect value caused by a defective component or circuit.
An air/fuel ratio of 14.7:1 is maintained under most driving conditions. Maximum engine RPM is limited by the DME/Motronic control unit by eliminating power to fuel injectors. The DME/Motronic control unit assumes control of the following functions.
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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.