The Anti-lock Braking System (ABS) fitted to Defender operates three features:
- Anti-lock braking
- Electronic Brake force Distribution (EBD)
- Traction Control (TC).
The anti-lock braking system (ABS) is controlled by the ABS ECU, which is located beneath the RH front seat. The ABS ECU receives wheel speed information from the wheel speed sensors and monitors deceleration when the brakes are applied. If wheel deceleration is outside expected values, the ABS ECU controls the brake line pressure to each wheel via the ABS modulator. Once wheel deceleration has recovered to within allow limits, the ABS ECU allows brake pressure to be re-applied to the wheels.
When the ignition is switched on, the ABS ECU carries out a system self checking process. When this has been successfully completed, the ABS will be fully functional.
Traction Control (TC) operates in a similar manner. The ABS ECU monitors the speed of each wheel during acceleration. If any wheel is rotating faster than the others, brake pressure is applied to that wheel to slow it to the speed of the remaining three wheels.
NOTE: TC can be disabled by operating the brake pedal ten times within ten seconds, when the ignition is turned on. TC will be re-activated when the ignition is turned off then on again.
The ABS also features an Electronic Braking force Distribution (EBD) function. EBD allows the brake balance between the front and rear wheels to be maintained at an optimum level, ensuring the rear wheels don't lock before the front wheels.
Operation
Power Distribution
Feed from the positive battery terminal (C0192) is supplied to fusible link 1 and fusible link 5 of the under seat fuse box (C0632) on an N wire. Fusible link 1 is connected in series with fusible link 4 and fuse 1, which are also located in the under seat fuse box. Fuse 1 (C0573) provides a constant battery feed to the ABS ECU (C0504) on an NW wire. Fusible link 4 (C0571) provides a constant battery feed to the ABS modulator pump relay (C0508) on an NW wire.
Fusible link 5 (C0570) is connected to the ignition switch (C1043 on LHD, C0028 on RHD) by an NW wire. When the ignition switch is turned to the 'ignition' position, current flows across the switch (C1732 on LHD, C0094 on RHD) to fuse 11 of the passenger compartment fuse box (C0580) on a W wire. Fuse 11 (C0580) provides an ignition feed to the ABS ECU (C0504) on a GO wire.
Wheel Speed Sensors
The wheel speed sensors provide the ABS ECU with 60 pulses per wheel revolution. Each wheel speed sensor is connected to the ABS ECU via a twisted pair of wires, with both wires carrying the pulsed signal to the ABS ECU. The sensors are connected to the ABS ECU (C0505) as follows:
- The LH front wheel speed sensor (C0516) is connected to the ABS ECU via a pair of W wires.
- The RH front wheel speed sensor (C0517) is connected to the ABS ECU via a pair of G wires.
- The LH rear wheel speed sensor (C0502) is connected to the ABS ECU via a pair of W wires.
- The RH rear wheel speed sensor (C0503) is connected to the ABS ECU via a pair of G wires.
ABS Modulator Pump
The ABS modulator pump is part of the modulator assembly, and is controlled by the ABS ECU. The pump is used to increase brake line pressure. The ABS ECU (C0506) provides a feed to the modulator pump relay coil (C0508) on a WO wire. The relay coil (C0508) is earthed on a B wire. The energised modulator pump relay (C0508) allows a battery feed from fusible link 4 of the under seat fuse box (C0571) to power the modulator pump (C1587 on LHD, C0507 on RHD) on an NR wire. The pump is earthed on a B wire.
The energised modulator pump relay (C0508) also provides a feed to the ABS ECU (C0504) on an NR wire. This feed is used by the ABS ECU to monitor operation of the modulator pump.
ABS ECU and Modulator
The ABS ECU (C0506) provides outputs to the ABS modulator (C1591 on LHD, C0501 on RHD) as follows:
- The ABS modulator LH front outlet valve is driven by the ABS ECU via an SW wire.
- The ABS modulator LH front inlet valve is driven by the ABS ECU via an SR wire.
- The ABS modulator RH front outlet valve is driven by the ABS ECU via an SG wire.
- The ABS modulator RH front inlet valve is driven by the ABS ECU via an SU wire.
- The ABS modulator LH rear outlet valve is driven by the ABS ECU via an SY wire.
- The ABS modulator LH rear inlet valve is driven by the ABS ECU via an SN wire.
- The ABS modulator RH rear outlet valve is driven by the ABS ECU via an SP wire.
- The ABS modulator RH rear inlet valve is driven by the ABS ECU via an SK wire.
The ABS ECU (C0504) and the modulator (C1592 on LHD, C0500 on RHD) are both earthed on B wires.
The ABS modulator (C1591 on LHD, C0501 on RHD) provides outputs to the ABS ECU (C0506) as follows:
- An earth monitoring signal is provided to the ABS ECU on a B wire.
- A brake pedal signal is provided to the ABS ECU on an RB wire.
Engine Control Module
The Engine Control Module (ECM) provides information to the ABS ECU to enable optimum TC performance. The ECM (C0658) is connected to the ABS ECU (C0504) as follows:
- The ECM provides the ABS ECU with a Pulse Width Modulated (PWM) signal on an SP wire. This signal includes information on engine torque, engine throttle, engine type, and throttle type.
- The ECM provides the ABS ECU with pulsed voltage signal on a YK wire. This signal informs the ABS ECU of engine speed. The ECM provides the ABS ECU with two voltage pulses per engine revolution.
Instrument Pack
ABS Warning Lamp
The ABS ECU (C0504) provides a feed to the instrument pack mounted ABS warning lamp (C0230) on an RS wire. The ABS ECU illuminates the warning lamp under the following conditions:
- A bulb check when the ignition is switched on. The ABS ECU illuminates the lamp for 0.3 seconds.
- If vehicle speed remains under 7 kph (4.3 mph) after the ignition has been switched on. When vehicle speed is greater than 7 kph, the ABS ECU will extinguish the lamp.
- If a fault has been stored in the ABS ECU memory.
TC Lamp
The ABS ECU (C0504) provides a feed to the instrument pack mounted TC lamp (C0230) on a YS wire. The ABS ECU illuminates the lamp under the following conditions:
- A bulb check when the ignition is switched on. The ABS ECU illuminates the lamp for 0.3 seconds.
- For a minimum of 2 seconds if TC is active.
- If a TC fault is detected by the ABS ECU.
NOTE: The TC lamp may also illuminate if an ABS fault is detected.
Brake Warning Lamp
The ABS ECU (C0504) provides a feed to the instrument pack mounted brake warning lamp (C0230) on a BW wire. The ABS ECU illuminates the lamp under the following conditions:
- A bulb check when the ignition is switched on. The ABS ECU illuminates the lamp for 3 seconds.
- If an EBD fault is detected by the ABS ECU.
The brake warning lamp will also illuminate if the handbrake is applied, or the brake fluid level is low. The handbrake switch (C0091) is connected to the brake warning lamp (C0230) by a WY then BW wire. The brake fluid level switch (C1725 on LHD, C0026 on RHD) is connected to the brake warning lamp (C0230) by a BW wire.
Diagnostic Socket
The ABS ECU can be interrogated using TestBook via the diagnostic socket. The diagnostic socket (C0040) is located on the centre console, and is connected to the ABS ECU (C0504) by a K wire.