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.
Central Electronic Module (CEM) (2001-2004): Function: Horn
The horn is operated when the steering wheel module (SWM) (3/130) receives a signal from the switches (3/37) in the steering wheel. The steering wheel module (SWM) sends data to the central electronic module (CEM) (4/56) via the control area network (CAN) indicating that the switch is closed. The central electronic module (CEM) activates the relay (2/17) for power supply to the horn.
There is also a signal directly connected from the steering wheel module (SWM) to the central electronic module (CEM). This is used if there is a fault in the control area network (CAN). This is a Limp-Home function.
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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.