Antilock Brakes / Traction Control Systems: Description and Operation

ANTI-LOCK BRAKING SYSTEM (ABS)

DESCRIPTION

General
The ABS is a full time, four channel system that gives individual speed control to all four wheels to provide the vehicle with anti-lock braking (ABS), Electronic Traction Control (ETC), and Hill Descent Control (HDC). The systems are controlled by the ABS ECU, which is mounted on the rear of the ABS modulator. The ABS ECU also controls the front to rear brake balance by Electronic Braking force Distribution (EBD). This maximises vehicle stability under braking.

The ABS modulator uses the CAN-BUS to communicate with other ECU's to enable it to control braking more efficiently.

OPERATION

General
Feed from the positive battery terminal (C0192) is supplied to fusible link 1, fusible link 3, fusible link 8, and fusible 11 (C0632) on an R wire. All are located in the engine compartment fuse box.

Fusible link 8 (C0574) and fusible link 11 (C0570) provide constant battery feeds to the ABS modulator (C0501) on NK and NR wires respectively. The ABS modulator (C0501) is earthed on a pair of B wires.

Fusible link 1 is connected in series with fusible link 2, which is also located in the engine compartment fuse box. Fusible link 2 (C0571) provides a feed to the ignition switch (C0028) on an NR wire. Fusible link 3 (C0571) also provides a feed to the ignition switch (C0028) on an N wire.

When the ignition switch is turned to the 'ignition' position, current flows across the switch (C0028) to fuse 2 of the passenger compartment fuse box (C0588) on an NW wire. When in the 'ignition' position, the ignition switch (C0028) also provides a feed to fuse 7 and fuse 35 of the passenger compartment fuse box on a G wire.

Fuse 2 of the passenger compartment fuse box (C0580) provides an ignition feed to the brake pedal switch (C0075) and the HDC relay (C0574) on G wires. Fuse 35 (C0580) provides an ignition feed to the hill descent switch (C0365 on manual transmission vehicles, C0878 on automatic transmission vehicles), and the hill descent relay (C0571) on W wires. Fuse 7 (C0582) provides an ignition feed to the ABS ECU (C0501) on a W wire.

Wheel Speed Sensors
The ABS ECU (C0501) supplies a feed to all tour wheel speed sensors as follows:
^ To the LH front wheel speed sensor (C0516) on an R wire.
^ To the RH front wheel speed sensor (C0517) on a Y wire.
^ To the LH rear wheel speed sensor (C0502) on a G wire.
^ To the RH rear wheel speed sensor (C0503) on a W wire.

The wheel speed sensors provide the ABS ECU with a square wave form signal. By measuring the frequency of the wave form, the ABS ECU can calculate the speed of the road wheel. The sensors provide the ABS ECU (C0501) with wheel speed signals as follows:
^ From the LH front wheel speed sensor (C0516) on an RB wire.
^ From the RH front wheel speed sensor (C0517) on a YB wire.
^ From the LH rear wheel speed sensor (C0502) on a GB wire.
^ From the RH rear wheel speed sensor (C0503) on a WB wire.

It the ABS ECU detects wheel deceleration is too great, it will initiate the ABS. It the ABS ECU detects that wheel speed is greater than vehicle speed, it will initiate ETC. If HDC is operational, the ABS ECU will control vehicle speed at 7 mph (11 km/h) by applying the brakes where necessary.

ABS ECU

Td4 - Manual Transmission
The ABS ECU (C0501) provides a road wheel speed signal to the Engine Control Module (ECM) (C0331) via the CAN BUS on YN (low) and YB (high) wires.

Td4 - Automatic Transmission
The ABS ECU (C0501) provides a road wheel speed signal to the Automatic Transmission Control Unit (ATCU) (C0932) via the CAN BUS on YN (low) and YB (high) wires.

K1.8
The ABS ECU (C0501) provides a road wheel speed signal to the Engine Control Module (ECM) (C0913) via the CAN BUS on YN (low) and YB (high) wires.

KV6 - NAS
The ABS ECU (C0502) provides a road speed signal to the ATCU (C0932) via the CAN BUS on YN (low) and YB (high) wires. This information is relayed to the ECM (C0331) via the CAN BUS on YN (low) and YB (high) wires.

KV6 - ROW
The ABS ECU (C0500 on 01MY vehicles, C0501 on 02MY vehicles) provides a road wheel speed signal to the ATCU (C0932) via the CAN BUS on YN (low) and YB (high) wires. This information is relayed to the ECM (C0371) via the CAN BUS on YN (low) and YB (high) wires.

For more information on the CAN BUS, refer to the Communication Databuses.

Brake Pedal Switch
The brake pedal switch is a double contact mechanical switch, mounted at the top of the brake pedal adjacent the brake pedal sensor. The switch (C0075) is provided an ignition feed from fuse 2 of the passenger compartment fuse box (C0580) on a G wire. When the brake pedal is at rest, the switch (C0075) provides a feed to the ABS ECU (C0501) on a GR wire. When the brake pedal is pressed, the switch (C0075) informs the ABS ECU (C0501) by providing a feed on a GP wire.

When the brake pedal is pressed, the switch (C0075) also provides a feed to the following on GP wires:
^ The LH brake lamp (C0121).
^ The RH brake lamp (C0125).
^ The Center High Mounted Stop Lamp (CHMSL) (C0613).

Accelerometer
The accelerometer is mounted beneath the center console adjacent the handbrake, and provides the ABS ECU additional information regarding vehicle motion. The ABS ECU (C0501) provides a feed to the accelerometer (C1220) on a Y wire. The sensor (C1220) returns a vehicle acceleration/deceleration signal to the ABS ECU (C0501) on an R wire.

The accelerometer (C1220) is provided an earth path via the ABS ECU (C0501) on a U wire.

Brake Fluid Level Switch
The ABS ECU (C0501) provides a feed to the brake fluid level switch (C0026) on a BW wire. The switch is closed when the correct amount of brake fluid is present in the brake fluid reservoir. The switch (C0026) is earthed on a B wire. If the brake fluid level drops below the recommended level, the switch contacts open. When the ABS ECU registers the switch opening, it informs the instrument pack to illuminate the brake fluid warning lamp via the CAN-BUS.

Hill Descent Control (HDC)

HDC Switch (Manual Transmission)
The HDC switch (C0365) is mounted on the gear lever, and informs the ABS ECU (C0501) when HDC has been selected. When HDC is selected, the switch contacts close, and a feed is provided to the ABS ECU (C0501) on a PS wire. When the ABS ECU receives this feed, it energizes the HDC relay.

HDC Switch (Automatic Transmission)
The HDC switch (C0878) is mounted on the center console, and informs the ABS ECU (C0501) when HDC has been selected. When HDC is selected, the switch contacts close, and a feed is provided to the ABS ECU (C0501) on a PS wire. When the ABS ECU receives this feed, it energizes the HDC relay.

NOTE: The ABS ECU Will only initiate HDC if either 1st or reverse gear are selected, and brake temperature doesn't exceed 400 °C (752 °F).

HDC Relay
The HDC relay (C0575) is located in the engine compartment fuse box, and is controlled by the ABS ECU (C0501) on a BR wire. When energized, the HDC relay (C0570) provides a feed to the following on GP wires:
^ The ABS ECU (C0500 on 01MY vehicles, C0501 on 02MY vehicles).
^ The LH brake lamp (C0121).
^ The RH brake lamp (C0125).
^ The CHMSL (C0613).

Diagnostic Socket
The diagnostic socket (C0040) is connected to the ABS ECU (C0501) by a K wire, enabling the ABS ECU to be interrogated by Test Book or T4.