Immobilization ECU
The immobilization ECU is installed on the driver's side of the gear selector assembly, underneath the center console. When it detects a valid transponder/ignition key in the ignition switch and is receiving a release signal from the steering lock ECU, the immobilization ECU sends a release signal to the ECM and energizes the starter solenoid when the ignition switch is turned to crank. The release signal to the ECM is a further rolling code synchronized in the immobilization ECU and the ECM. If either the ECM or the immobilization ECU are replaced they have to be re-synchronized using T4.
Up to 10 different transponders can be used with the immobilization ECU. The 10 unique transponder key codes and their associated rolling codes are generated during vehicle production and programmed into the immobilization ECU. The transponder of each ignition key supplied with the vehicle is then programmed with one of the key codes and its associated rolling code. Once the immobilization ECU and the transponders have been programmed they cannot be over written. The 'spare' key codes and associated rolling codes are retained in the immobilization ECU for future use. The key codes and associated rolling codes are also recorded in a spares support database together with the Vehicle Identification Number (VIN).
If an ignition key is lost, the key code of the related transponder should be disabled in the immobilization ECU using T4. If the key is subsequently found, the transponder can be enabled again.
If a replacement or additional ignition key is ordered, the transponder of the new ignition key is programmed by the spares supplier with one of the spare key codes and associated rolling code from the spares support database. The immobilization ECU recognizes the first use of the key code and automatically enables the new ignition key.
When a replacement immobilization ECU is ordered it comes pre-programmed with the key codes and rolling codes from the spares support database ready for use with the existing ignition keys once it has been synchronized with the ECM.
A starter motor protection function is incorporated into immobilization ECU. When the engine speed exceeds a predetermined value, a relay inside the immobilization ECU is disabled. This prevents damage to the starter motor in the event of a sticking ignition switch or if crank is selected while the engine is running.
The immobilization ECU is powered by a permanent battery feed from the passenger compartment fusebox. It also receives an auxiliary power feed and an ignition power feed from the ignition switch. Power for the starter motor solenoid is supplied to the immobilization ECU when the ignition switch is in the crank position (on Td6 models) or on a permanent feed from the passenger compartment fusebox (on V8 models). A connection with the K bus provides the immobilization ECU with engine speed and locking system status.