Security (Operation): Description and operation

Operation

Immobilisation System

The immobilisation system prevents unauthorised starting of the vehicle. The immobilisation ECU is a secure interface between the ECM which cannot be copied or by-passed.

Immobilisation ECU The ECU ensures that the vehicle is in a safe condition to start the engine. On vehicles with automatic gearbox, the ECU prevents starter operation if the gearbox is not in park or neutral. A feed from the automatic transmission solenoid (C0024) is connected to pin 3 on the immobilisation ECU. The feed is only present when the selector lever is in either park/neutral. If the selector lever is moved to any other position the feed to the immobilisation ECU is removed and engine cranking will be disabled.

When the ignition is switched 'off' and the key removed from the switch, the immobilisation ECU becomes active and prevents unauthorised starter operation. Re-mobilisation is achieved by insertion of the vehicle key into the ignition switch and the switch turned to 'AUX' position I.

Ignition Switch Transponder Coil and Key Transponder The coil is supplied with a modulated electric current from the immobilisation ECU. When the key transponder is within 2 cm (0.78 in) from the coil, with the ignition switch in the 'AUX' position, an energy transfer from the coil to the transponder takes place, similar to the transformer principle, at a frequency of 125 kHz. The ECU de-modulates and decodes the received data and compares this with identification code data from the ECM. If the data is correct the ECU allows starter operation.

When the key is inserted in the ignition switch, the key transponder transmits three separate pieces of information to the ECU via the transponder coil: l A unique key identification number which is passed to the ECU l A unique key password used by the ECU to communicate with the transponder l Confirmation that the rolling code from the transponder is correct to the rolling code stored by the ECU

Programming The immobilisation ECU is programmed with vehicle specific data during manufacture. The key transponders are supplied with the specific vehicle preprogrammed with the mechanical code for that vehicle's lockset. The mechanical code is read at the factory before the keys are programmed and the information is stored in a central database. The data is required to cut spare or replacement keys.

The ECU is programmed during manufacture with data to support up to ten keys. The programmed information is recorded against the VIN for that vehicle and stored in a central database.

Replacement or spare keys will be ordered and delivered to the dealer already programmed with the correct information specific to the particular vehicle and ready for use.

If a replacement immobilisation ECU is required it will be ordered and delivered to the dealer programmed with the original information stored during manufacture. The ECM will not require reprogramming because the replacement ECU will have the same identification code as before. The ECM and the EWS-3D immobilisation ECU will however need have their rolling code synchronised using TestBook.

If the ECM is replaced, the ECM will have to learn the identification code. This is achieved using TestBook. When the immobilisation ECU receives the correct diagnostic message it will transmit the identification code on a continual basis until the ignition is switched off. Simultaneously, the ECM is also receives a diagnostic command to learn the new code.

Starter Motor Protection The immobilisation system incorporates a starter motor protection function. When the engine speed exceeds a predetermined value, a starter relay inside the EWS-3D ECU is disabled. This relay is wired in series with the main starter motor solenoid and therefore when disabled it cuts off the power supply to the starter motor. This prevents damage to the starter motor being caused by a sticking ignition switch. The engine speed is derived from the instrument pack which converts the speed from a CAN bus signal into a pulsed signal compatible with the EWS-3D ECU.