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.
Repair and Diagnosis: Electrical: Starter: Starters: Operation
On 7-series and 540i with automatic transmission, starter is controlled by Digital Motor Electronic (DME) control module. After the DME control unit receives the input signals from the ignition switch and neutral safety switch, it energizes the starter relay, which in turn energizes terminal No. 50 at the starter motor. After the DME control unit receives a signal from the crankshaft position sensor that the engine is running (920 RPM cold; 680 RPM at normal operating temperature), the DME control unit switches off the starter relay.
On all other models, starter is controlled by electronic immobilizer control unit. Turning ignition switch to START position energizes terminal No. 3 at electronic immobilizer control unit. When clutch is depressed (M/T) or gear selector is in Park or Neutral (A/T), a signal is sent to terminal No. 9 at electronic immobilizer control unit. When both these signals are received by electronic immobilizer control unit, terminal No. 50 is energized at starter motor.
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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.
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