ABS Modulator Schematic (From 2002 MY) (Brakes) (page 2 of 2)

ABS ECU The ABS ECU controls the operation of the ABS modulator to provide the ABS, ETC and HDC functions. It also operates warning lamps in the instrument pack to provide the driver with status information on each function. The ABS ECU is attached to the ABS modulator. Incorporated into the ABS ECU are integrated circuits and software for system control and diagnostics. An electrical connector interfaces the unit with the vehicle wiring.

The warning lamps consist of: l An amber ABS graphic. l An amber ETC graphic. l Two inclined vehicle graphics for HDC, one amber (fault), which includes an exclamation mark, and one green (information).

The warning lamps are Light Emitting Diodes (LED) installed on the printed circuit board of the instrument pack and cannot be replaced separately.

When the ignition is switched on, the ABS ECU performs a 'bulb' check of the warning lamps as part of the power up procedure. If a warning lamp remains illuminated after the bulb check, a fault has been detected and repair action is required. On a serviceable system: l The ETC and HDC warning lamps are extinguished after 2 to 3 seconds. l Up to 2002 MY, the ABS warning lamp is extinguished briefly, after 1.3 to 2 seconds, then remains illuminated until vehicle speed exceeds 4.4 mph (7 km/h). l From 2002 MY, the ABS warning lamp is extinguished briefly, after 1.3 to 2 seconds, is illuminated again for a further 0.5 second and then extinguished.

The ABS ECU continually calculates vehicle speed using the inputs from all four ABS sensors. Vehicle speed is used as a reference against which individual wheel speeds are monitored for unacceptable acceleration or deceleration. Vehicle speed is also output to the instrument pack for the speedometer.