Although a key is used in the normal way to lock and unlock the vehicle, this will not arm the alarm system. The system is armed with an RF handset, which transmits a rolling code. This code is received by the alarm ECU, which is mounted behind the instrument pack.
The alarm system fitted to 1999 MY Defenders has two methods of protecting the vehicle; perimetric protection, and volumetric protection.
Perimetric protection monitors the hinged panels of the vehicle; the bonnet, the tail door, the drivers door, and all passenger doors. If any of these panels are opened without the alarm ECU receiving the correct signal from the RF handset, the alarm will be triggered.
Volumetric protection monitors the interior space within the passenger compartment. When the alarm is armed, the volumetric sensor (mounted in the headlining above the RH ’B’ post) will sense any movement and trigger the alarm.
The alarm ECU also interacts with the Engine Control Module (ECM), causing the engine to be immobilised whenever the alarm is armed. See Engine Immobilisation.
Operation
The battery positive terminal provides a feed to the engine compartment fuse box (C0632-1) on a brown wire. Fuse 6, fuse 7, fusible link 5 and fusible link 6 are all connected in parallel and provide a direct battery feed to the following;
- Fuse 6 (C0574-2) provides two feeds to the alarm ECU on purple/brown wires. The first (C0061-25) is used as a power signal. The second (C0057-8) is used to power the indicator lamp circuits (C0057-1 & C0057-6) on green/white (RH indicators) and green/red (LH indicators) wires respectively.
- Fuse 7 (C0574-1) provides a feed to the front interior lamp (C0355-3) on a purple/brown then purple wire.
- Fusible link 5 (C0570-2) provides a feed to the BBUS (C0666-2) on a brown then black wire, and the ignition switch (C0028-1) on a brown/white wire.
- Fusible link 6 (C0571-3) provides feeds to the alarm relay (C0731-6 & C0731-8) on brown/blue wires, and the alarm LED (C1060-6) also on a brown/blue wire.
The alarm ECU receives arm and disarm commands from the RF handset via an aerial. The aerial (C1136-1) is connected to the alarm ECU (C0061-26) by a orange/slate wire. When the alarm ECU is disarmed and the ignition switch is set to the crank position, it provides an earth path (C0057-10) for the starter relay (C0151-6) on a black/orange wire. This will enable the engine to be started. See Charging and Starting.
The Alarm ECU (C0061-14) also communicates with the ECM (C0658-34). It sends a pulsed voltage signal along a light green/slate wire to control engine immobilisation. The alarm ECU (C0057-12) also sends a constant battery feed to the passive coil (C0049-2) on an orange/purple wire. A second pulsed voltage signal is sent by the alarm ECU (C0057-7) to the passive coil (C0049-1) on an orange/green wire. See Engine Immobilisation.
The alarm ECU is connected to all the door switches (including the tail door) and the bonnet switch. When the perimetric alarm system is armed, the ECU monitors the switch circuits and detects open or grounded circuit. By monitoring the circuits in this way, the alarm ECU can tell if any of the hinged panels are open or closed. The alarm ECU is connected to the following switches;
- The alarm ECU (C0061-5) to the RH front door switch (C0054-1) on a slate/white wire.
- The alarm ECU (C0061-16) to the LH front door switch (C0033-1) and the tail door switch (C0615-1) on purple/blue wires.
- The alarm ECU (C0061-16) to the RH rear door switch (C0111-1) on a purple/blue wire.
- The alarm ECU (C0061-16) to the LH rear door switch (C0112-1) on a purple/blue wire.
- The alarm ECU (C0061-9) to the bonnet switch (C0007-2) on a orange/blue wire.
When the doors and bonnet are closed, the switches are open. If any door is opened, the respective switch closes to earth through the fixings. If the bonnet is opened the switch (C0007-1) is earthed on a black wire. For volumetric protection, when the alarm is armed, the alarm ECU (C0061-20) provides a feed to the volumetric sensor (C0719-1) on a black/brown wire. The sensor (C0719-2) is earthed on a black wire via the earth header (C0550-1). When the alarm system is armed, the volumetric sensor (C0719-3) sends a constant voltage signal back to the alarm ECU (C0061-3) on a white/black wire. If the volumetric sensor is triggered, this changes to a pulsed signal. The alarm ECU, recognising this fluctuation in voltage, triggers the alarm.
When the alarm is activated, the alarm ECU (C0057-5) provides an earth for the alarm relay (C0731-4) on an orange/white wire. Current flows across the relay switch (C0731-6 & C0731-2) and onto the alarm sounder (C0520-2) on a orange/black wire. The alarm sounder (C0520-1) is earthed on a black wire.
The energised alarm relay (C0731-5) also provides a feed to fuse 20 of the passenger compartment fuse box (C0581-20) on an orange/red wire. Fuse 20 (C0581-19) then supplies a feed to the LH (C0003-2) and RH horns (C0004-2) on purple/black wire.
By switching the earth path on and off, the alarm ECU can control the operation of the sounder and the horns.
The alarm ECU (C0057-4) supplies a feed to the anti-theft alarm LED (C1060-3) on a pink wire. Because the potential difference across the LED is 0 volts, the LED fails to illuminate.
To illuminate the LED, the alarm ECU (C0057-4) withdraws the feed on the pink wire, and provides a path to earth. Current can now flow and illuminate the LED. The alarm ECU can control the flashing sequence of the LED by switching the feed/earth on the pink wire.
Depending on market, some vehicles are also fitted with a BBUS. The BBUS has its own internal power supply. Should the vehicle battery or the sounder be disconnected, the BBUS will sound for approximately 4 1 /2 minutes. To disconnect the vehicle battery without sounding the alarm See Repair Manual, Maintenance, Battery Condition.
The BBUS (C0666-2) is supplied constant battery voltage from fusible link 5 (C0570-2). The BBUS (C0666-4) is earthed via earth header 550. A battery voltage signal is also supplied to the BBUS (C0666-3) from the alarm ECU (C0057-5). When the alarm is triggered, the alarm ECU withdraws this feed, and the BBUS sounds.
The BBUS (C0666-1) also receives an ignition feed from fuse 1 of the passenger compartment fuse box (C0580-2) on a white/green then black wire. All connections to and from the BBUS are on black wires.
The alarm ECU also controls the operation of the interior lamps. See Interior Lamps.