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)
The central electronic module (CEM) (4/56) is the master unit for the immobilizer. The central electronic module (CEM), steering column lock module (SCL), start control module (SCU) and the engine control module (ECM) are linked by codes. The central electronic module (CEM) is also programmed with codes for each ignition key that belongs to the vehicle.
If the vehicle has an alcolock (option 2008-) installed, the code in the handset unit must also be programmed into the Central electronic module (CEM) to work. The signal from the alcolock handset is received by the Remote Receiver Module (RRX), which forwards the signal to the Central electronic module (CEM).
The central electronic module (CEM) transits commands and signals to the other control modules included in the system. The identity of the remote key is checked by the central electronic module (CEM) via the start control module (SCU) or by the keyless vehicle module (KVM) via the antennas (only vehicles with the keyless locking system). Which control module that validates the remote key depends on whether the vehicle is being started passively or not. There is a communication circuit in the remote key, known as a transponder. The transponder has a unique identification code that must be learned by the central electronic module (CEM) before the remote key can be used to start the vehicle. This learning process takes place during installation at the factory. New remote keys can be added afterwards.
If there is a keyless vehicle module (KVM) installed in the vehicle, the central electronic module (CEM) requests that it checks the identity of the remote key when:
- the starter button is pressed
- the clutch pedal is depressed (MAN)
- the brake pedal is depressed (AUT).
The central electronic module (CEM) controls the relay for the fuel pump (FP). When the identity of the remote key and all included components have been checked, the central electronic module (CEM) activates the fuel pump (FP) after a command from the engine control module (ECM).
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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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