Circuit Description

How the Circuit Works ('97-'99 Models)

The anti-lock brake system (ABS) prevents locking of the wheels as a result of heavy braking and/or poor traction. A vehicle with locked wheels cannot be steered. The anti-lock brake system controls the application of the brakes, allowing the driver to maintain control of the steering.

Under anti-lock conditions, the anti-lock brake system (ABS) modulates the pressure of the brake fluid to each brake caliper. This system is a four channel system: the pressure at each caliper is controlled independently of the pressure at any other caliper. Whenever a wheel is likely to lock during braking, the anti-lock brake system modulates the brake pressure at that wheel. When the brake pressure is reduced to the point where there is no longer any possibility of wheel locking, the system returns to the conventional braking system mode of operation.

Battery voltage is applied at all times through fuse 32 and fuse 40 to the ABS control unit. When the ignition is in ON (II), battery voltage is supplied to the control unit through fuse 4. The control unit is case grounded. Inputs are received from the brake switch, alternator, brake indicator light, the individual wheel sensors located at each wheel, and from the ABS pressure switch. With the charging and brake systems functioning correctly the control unit can activate the fail-safe relays, modulator solenoids, and ABS pump motor on demand. The ABS control unit uses the inputs from the brake switch and wheel speed sensors to control the modulator solenoid unit. The solenoids adjust the hydraulic pressure applied to each caliper.

The ABS control unit has a self-diagnosis function. When the self-diagnosis function detects a fault, the control unit turns on the "ABS" indicator and disables the anti-lock brake system. If the fault is not in the conventional braking system, the brakes will continue to operate normally but without the anti-lock feature.