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.
Control Module
The most important task of the upper electronic module is to manage the following functions:
- Siren (SCM)
- Sun roof
- Movement sensor (MMS)
- Rain sensor (RSM)
- Interior roof lighting
- Sun visor lighting
- Remote control
- Automatic rear view mirror anti-dazzle
- Seat belt reminder
- Tire pressure warning
- Indication of disconnected passenger airbag (PAD - Passenger Airbag Deactivated)
- Compass
The control module is integrated in the rear view mirror. If the control module is replaced, the rear view mirror assembly must also be replaced.
The upper electronic module (UEM) communicates with directly connected components and with other control modules and components via serial communication and the controller area network (CAN).
The control module checks activations and input and output signals through an integrated diagnostic system A diagnostic trouble code (DTC) is stored if the control module detects an error. In certain cases the upper electronic module replaces the faulty signal with a substitute signal.
Diagnostic trouble codes (DTC) are stored in the control module memory. The data can be read off using the appropriate diagnostics tool.
A simple way to check that the upper electronic module is supplied with power is to activate the seat belt reminder function Activate the seat belt reminder by sitting in the driver's seat. Switch on the ignition, do not fasten the seat belt. If the seat belt reminder lights, the upper electronic module is supplied with voltage. Another way of checking that the upper electronic module is supplied with voltage is to switch on the rear reading lamps.
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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.