Engine immobilisation - Td5 (page 2 of 2)

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.