Control Unit
The immobiliser control unit is attached to the ignition lock.
In vehicles with airbags or with height-adjustable steering wheels, a differently shaped control unit is used for design reasons. The two control units are however technically identical.
The immobiliser control unit antenna is arranged in a ring around the ignition lock.
When the transponder key is inserted in the ignition lock, the transponder enters the very limited reception range of the antenna.
This guarantees that only the key that is inserted in the ignition lock can have its transponder code transferred. This excludes the possibility of interference from other transponder keys in the vehicle.
Once the ignition is switched on, voltage is set to the immobiliser control unit antenna (consisting of a coil),whereby, according to the transponder principle, the supply voltage is electro-magnetically transferred (induced) to the transponder.
The code sent by the transponder key is received by the immobiliser control unit via the antenna and compared with the stored codes.
The immobiliser control unit is programmed as standard with two transponder codes, corresponding to the two keys supplied with the vehicle. A maximum of 5 transponder codes can be stored.
At the same time (ignition ON), the engine control unit sends a signal to the immobiliser control unit SM1 (Ter. 2), requesting transfer of the coded signal of approval (imo signal).
Once the transponder codes from the transponder key has been recognised, the immobiliser control unit SM2 (Ter. 7) passes the imo signal to the engine control unit for comparison (for vehicles with petrol or 25 DT diesel engines). In diesel engines without electronic engine management, the imo signal is transferred to the fuel cutoff
solenoid valve.
If the imo signals from the immobiliser control unit and the engine control unit or fuel cutoff solenoid valve do not match, all relevant engine functions are switched off by the engine control unit or the diesel feed is blocked.
The engine can be started during the transfer and evaluation phase for the transponder code and the imo signal to prevent delays.
If the codes do not match, the engine is switched off again if already running.
The following codes/data are stored in the immobiliser control
unit's reference memory in vehicle production:
· Security code
· Engine type
· Mechanical key number
· Vehicle identification number
· Transponder code
The security code cannot be deleted or altered with TECH 1.
The transponder code and the engine type are processed internally only and are not displayed on TECH 1.
The vehicle identification number and the mechanical key number are stored as further important information for identification of the vehicle and can be displayed on TECH 1.