The engine immobilisation system fitted to 1999 MY Defender works in conjunction with the Alarm system. The alarm ECU sends a coded signal to the Engine Control Module (ECM). If the signal does not match the one expected by the ECM, the ECM will immobilise the engine.
Passive immobilisation is also fitted, with a passive coil fitted around the ignition barrel. This will activate 30 seconds after the ignition is turned off and the drivers door is opened. Alternatively, passive immobilisation will occur 5 minutes after the vehicle is unlocked, or the ignition is turned off. When attempting to restart the vehicle, passive immobilisation can be switched off using either the RF handset or EKA code.
Operation
Feed from the battery positive terminal is connected to fusible link 5 and fuse 6 of the engine compartment fuse box (C0632-1) by a brown wire. Fusible link 5 and fuse 6 are connected in parallel. Fuse 6 (C0574-2) supplies a constant battery feed to the alarm ECU (C0061-25) on a purple/brown wire. Fusible link 5 (C0570-2) supplies a feed to the ignition switch (C0028-1) on a brown/white wire.
When the ignition switch is turned to position ’II’, current flows across the switch (C0094-1) to fuse 1 of the passenger compartment fuse box (C0580-1) on a white wire. Fuse 1 (C0580-2) supplies an ignition feed to the alarm ECU (C0061-10) on a white/green wire. The alarm ECU (C0057-11) is earthed on a black wire.
When an ignition feed is received by the alarm ECU, it sends a coded signal (C0061-14) to the ECM (C0658-34) on a light green/slate wire. If the signal does not match the one expected by the ECM, the ECM will immobilise the engine.
When the ignition switch is turned to the crank position, current flows across the switch (C0090-1) to the starter relay (C0151-4) on a white/red wire. With the alarm ECU in the armed state, it also provides a feed (C0057-10) to the starter relay (C0151-6) on the black/orange wire. As the potential difference across the relay is 0 volts, the relay is not energized. When the alarm is de-activated, the alarm ECU (C0057-10) withdraws the feed on the black/orange wire, and provides an earth path (C0057-11) on a black wire. The starter relay will now be energized, enabling the engine to be cranked.
The alarm ECU (C0057-9) also controls the flashing sequence of the engine immobilisation warning lamp (C0233-5) by providing it with a pulsed signal on an orange wire. The lamp (C0230-8) is earthed on a black wire.
In addition to features directly controlled by the alarm ECU, a passive coil is fitted around the ignition barrel. This is a user friendly way of re-mobilizing the engine. The passive coil (C0049-1) receives a pulsed voltage signal from the alarm ECU (C0057-7) on an orange/green wire. The passive coil (C0049-2) also receives a constant feed from the alarm ECU (C0057-12) on an orange/purple wire.
The passive coil is only energized when the ignition switch is in position ’II’ and the engine is in an immobilised state. The coil creates a magnetic field that excites a coil in the RF handset. This causes the handset to transmit a code to the alarm ECU to re-mobilise the engine.
The alarm ECU can be interrogated via the diagnostic socket using TestBook. The socket (C0040-8) is connected to the alarm ECU (C0061-17) by an orange/light green wire.