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.
Switching on, function - GF67.29-P-2000GI
MODEL 163 as of 1.12.99
Function sequence
The rear window defroster can be switched on under the following conditions:
- Circuit 61 ON (engine operation recognition)
- Voltage not too low
The presence of c. 61 is connected to the engine compartment CAN bus as c. 61e information by the instrument cluster (A1) and read out by the extended activity module (EAM)(N10/1). C. 61 e ensures the presence of minimum engine speed and connection of the charge voltage. Thereby c. 61 e is a reliable criterion for recognizing when the engine is operating.
The rear window defroster switch (S21e9) is read in directly and evaluated by the extended activity module (EAM) (N10/1). When switching on, ground is connected to the input of N10/1 for a short time. N10/1 then connects ground to the rear window defroster indicator lamp (S21e2) and to the coil in the rear window defroster relay (F1k1).
The rear window defroster indicator lamp (S21e2) and the rear window defroster relay (F1k1) are actuated via separate lines by the extended activity module (EAM) (N10/1).
The rear window defroster relay (F1 k1) connects circuit 30 to the antenna splitter (A2/5). The antenna splitter (A2/5) then supplies the rear window defroster (R1) with electric heating current.
The extended activity module (EAM) (N10/1) also detects when the voltage is too low.
| Rear window defroster (RWD), function | GF67.29-P-0003GI | ||
| Rear window defroster (RWD), interlinkage of components | GF67.29-P-0003-02GI | ||
| Rear window defroster (RWD), location of components | GF67.29-P-0003-01GH | ||
| Switching off with switch, function | GF67.29-P-2002GI | ||
| Switching off after expiry of max. heating time, function | GF67.29-P-2003GI | ||
| Switching off with undervoltage, function | GF67.29-P-2005GI | ||
| Rear window defroster switch, location/purpose | GF67.29-P-3000GI | ||
| Rear window defroster relay, location/purpose | GF67.29-P-3001GI | ||
| Extended activity module, location/purpose/ design | GF54.21-P-4107GK |
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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.