Component Tests and General Diagnostics

WARNING: On surfaces which are soft and deep, for example deep powdery snow, sand or gravel, braking distance may be greater than with non-ABS braking. In these conditions, wheel lock and the build up of snow or gravel under wheels may be an aid to shorter stopping distance. However, it is still an advantage to maintain the stability and maneuverability available with ABS control.

NORMAL OPERATION
1. With ignition switch in On position, the system will automatically carry out self test function. This will be felt as a slight movement in brake pedal and a short, rapid series of clicks indicating that solenoid valves have been checked.
2. Observe warning lights, ensure parking brake/fluid warning light extinguishes after initial bulb check or when parking brake is released, indicating that power assistance is available. Time taken to pressurize system is up to 40 seconds.
3. Start vehicle and drive away. At 7 km/h (5 mph), the ABS warning light must be extinguished.
4. In road conditions where surface friction is sufficient to slow or stop the vehicle without wheel lock, ABS does not operate.
5. In an emergency braking situation, if one or more wheels begin to slow rapidly in relation to vehicle speed, ABS will detect wheel locking tendency and will regulate brake pressure to maintain wheel rotation.
6. ABS operation will be felt as a vibration through pedal, at same time solenoid cycling will be heard.

WARNING: Constant pressure on foot pedal while ABS is operating is more effective than pumping the brakes. Do not pump brake pedal, this may reduce ABS efficiency and increase stopping distance.

7. Downward travel of pedal will also feel hard at point at which ABS operates. Little further pedal travel is possible at this point, but force on the pedal can be varied to influence braking force while ABS retains control.

BRAKE APPLICATION WITH PARTIAL FAILURE

WARNING:
^ IF A FAULT DEVELOPS IN THE BRAKE SYSTEM IT IS ESSENTIAL THAT IT IS INVESTIGATED IMMEDIATELY.
^ If, during braking, a drastically reduced resistance is detected at pedal and braking effectiveness is very much reduced, failure of the non-powered (master cylinder) portion of system is indicated. When this occurs DO NOT PUMP BRAKE PEDAL. Push the pedal through free movement to obtain braking effort from the power circuit. It is essential that brake pedal travel is not obstructed by items such as extra footwell mats.
^ FOOT PRESSURE ON THE PEDAL, USING MASTER CYLINDER ONLY, WILL NOT ACHIEVE THE SAME DEGREE OF BRAKING AS IS AVAILABLE FROM POWER ASSISTANCE.

1. When power assistance is not available, ABS braking is not operative. Both warning lights are illuminated. Braking effort is available from master cylinder only. This results in longer pedal travel and greater pedal effort required to decelerate vehicle.
2. If master cylinder fails, i.e. there is insufficient fluid in master cylinder to create pressure, braking to all four wheels is retained and ABS remains operative. The red warning light will be illuminated if cause of the master cylinder failure is a fluid leak and level in fluid reservoir is low enough to actuate fluid level switch.

CAUTION: Longer pedal travel is required, but power assisted braking is available at reduced efficiency.

3. If brake failure occurs due to a fractured brake pipe between a servo cylinder and a wheel, there may be no pressure in the master cylinder. The fluid warning light will illuminate when level in fluid reservoir is low enough to actuate fluid level switch. Master cylinder and power valve will operate as for master cylinder failure, but fluid from power circuit will push all moving parts in servo cylinder associated with failure to limit of travel. No pressurized fluid passes to the front brake caliper served by the affected servo cylinder, but pistons in rear calipers will be supplied with direct pressure from power valve. The front caliper served by the other servo cylinder retain braking as fluid from master cylinder is retained in servo cylinder not associated with the leakage.

CAUTION: Brake pedal travel will be greater and extra pedal effort will be required, accompanied by the vehicle pulling to one side.