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.
Rear Window "Defroster ON" Signal (Mark I Only)
On Mark I navigation systems, the magnetic field sensor (compass) can be falsely influenced by magnetic fields which are not from the earth's natural magnetic field. The magnetic field sensor is installed under the rear parcel shelf, which is in close proximity to the rear window defroster. This creates the need for a signal compensation when the rear defroster is switched on.
The compensation is derived from the dealership calibration procedures (see WORKSHOP HINTS ).
When the rear defroster is ON, the navigation computer receives the ON signal via the bus network. As the illustration shows, the signal is sent via the following pathway:
IHKA module > K-Bus > IKE > I-Bus > Video Module > ARCNET> Navigation
NO RELATED
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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.