The Anti-lock Braking System (ABS) is controlled by the ABS ECU, located under the RH front seat. The system comprises of the ECU, ABS wheel speed sensors on each wheel, and an ABS modulator.
Operation
Feed from the battery positive terminal is connected to fusible link 1 and fusible link 5 of the engine compartment fuse box (C0632-1) on a brown wire. Fusible link 1 is wired in series with fuse 2, which supplies a continuous battery feed (C0573-3) to the ABS ECU (C0504-1) on a brown/white wire.
Wired in parallel with fuse 2 is fusible link 4. Fusible link 4 (C0571-2) supplies a continuous battery feed to the ABS return pump relay (C0508-3) on a brown/white wire. At this stage, the relay is de-energised.
A continuous battery feed is also supplied to the ignition switch. Fusible link 5 (0570-2) is connected to the ignition switch (C0028-1) by a brown/white wire. With the ignition switch in position ’II’, current flows across the switch (C0094-1) to fuse 4 of the passenger compartment fuse box (C0580-1) on a white wire. Fuse 4 (C0580-8) supplies an ignition feed to the ABS ECU (C0504-2) on a green/orange wire.
The ABS ECU is earthed (C0504-12) on a black wire.
ABS modulator and ECU
The ABS ECU provides outputs to, and receives inputs from the ABS modulator as follows;
- Output from ABS ECU (C0506-1) to ABS modulator (C0501-1) to drive LH front outlet valve on a slate/white wire.
- Output from ABS ECU (C0506-2) to ABS modulator (C0501-2) to drive LH front inlet valve on a slate/red wire.
- Earth monitoring signal from ABS modulator (C0501-8) to ABS ECU (C0506-3) on a black wire.
- Output from ABS ECU (C0506-4) to ABS modulator (C0501-10) to drive RH front outlet valve on a slate/green wire.
- Output from ABS ECU (C0506-5) to ABS modulator (C0501-11) to drive RH front inlet valve on a slate/blue wire.
- Brake pedal input from ABS modulator (C0501-9) to ABS ECU (C0506-6) on a red/black wire.
- Output from ABS ECU (C0506-7) to ABS modulator (C0501-13) to drive LH rear outlet valve on a slate/yellow wire.
- Output from ABS ECU (C0506-8) to ABS modulator (C0501-12) to drive LH rear inlet valve on a slate/brown wire.
- Output from ABS ECU (C0506-10) to ABS modulator (C0501-5) to drive RH rear outlet valve on a slate/purple wire.
- Output from ABS ECU (C0506-11) to ABS modulator (C0501-4) to drive RH rear inlet valve on a slate/pink wire.
The ABS ECU also interacts with the Engine Control Module (ECM). The ECM (C0658-32) provides the ABS ECU (C0504-10) with a throttle position signal on a slate/purple wire. The ECM (C0658-19) also provides the ABS ECU (C0504-11) with an engine speed signal on a yellow/pink wire.
The ABS ECU can be interrogated using TestBook via the diagnostic connector. The diagnostic connector (C0040-7) is connected to the ABS ECU (C0504-5) by a pink wire. In the event of a failure, the ABS ECU (C0504-9) sends a feed to the brake fluid level warning lamp (C0230-14) on a black/white wire.
Wheel speed sensors
The ABS ECU also receives variable inputs from the four wheel speed sensors as follows;
- The LH front wheel speed sensor (C0516-1 & C0516-2) to the ABS ECU (C0505-1 & C0505-2 respectively) on a pair of white wires.
- The RH front wheel speed sensor (C0517-1 & C0517-2) to the ABS ECU (C0505-4 & C0505-5 respectively) on a pair of green wires.
- The LH rear wheel speed sensor (C0502-1 & C0502-2) to the ABS ECU (C0505-7 & C0505-8 respectively) on a pair of white wires.
- The RH rear wheel speed sensor (C0503-1 & C0503-2) to the ABS ECU (C0505-3 & C0505-6 respectively) on a pair of green wires.
ABS return pump
When the ABS functions operate, the ABS ECU (C0506-15) provides a feed to the ABS return pump relay (C0508-2) on a white/orange wire. The relay (C0508-4) is earthed on a black wire. This feed from the ABS ECU energises the relay, allowing the ignition feed to flow across the relay.
The ABS return pump relay (C0508-1) provides a feed to the ABS return pump (C0507-1) on a brown/red wire. The pump (C0507-2) is earthed on a black wire. The ABS return pump relay also provides a feed to the ABS ECU (C0504-8) on a brown/red wire. The ECU uses this signal to monitor the operation of the ABS return pump.
Instrument pack
The ABS ECU will inform the driver of any faults within the ABS or traction control systems (if fitted). The ABS ECU (C0504-9) supplies a feed to the brake fluid warning lamp (C0230-14) on a black/white wire if the level of fluid in the brake fluid reservoir reaches the minimum mark. The warning lamp (C0230-8) is earthed on a black wire.
If the ABS ECU detects a fault within the ABS system, it supplies a feed (C0504-18) to the ABS warning lamp (C0230-7) on a red/slate wire. The warning lamp (C0230-8) is earthed on a black wire.
If traction control is fitted, the ABS ECU (C0504-17) will illuminate the traction control warning lamp (C0230-16) by providing a feed on a yellow/slate wire if a fault is detected. The warning lamp (C0230-8) is earthed on a black wire.