The Anti-lock Brake System (ABS) is an option used on all models. It is an electronically operated, all wheel brake control system. Major components include the master cylinder, vacuum power brake booster, Electronic Control Unit (ECU), Hydraulic Control Unit (HCU) and various control sensors.
The brake system is a three channel design. The front brakes are controlled individually and the rear brakes in tandem.
The purpose of the Anti-lock Brake System (ABS) is to prevent wheel lock-up under heavy braking conditions on virtually any type of road surface. ABS is desirable because a vehicle which is stopped without locking the wheels will retain directional stability and some steering capability. This allows the driver to retain greater control of the vehicle during heavy braking.
Under normal braking conditions, the ABS functions the same as a standard brake system with a diagonally split master cylinder and conventional vacuum assist.
If wheel locking tendency is detected during application, the system will enter anti-lock mode. During anti-lock mode, hydraulic pressure in the four wheel circuits is modulated to prevent any wheel from locking. Each wheel circuit is designed with a set of electrical valves and hydraulic line to provide modulation, although for vehicle stability, both rear wheel valves receive the same electrical signal. The system can build or reduce pressure at each wheel, depending on signals generated by the Wheel Speed Sensors (WSS) at each wheel and received at the Controller Anti-lock Brake (CAB).
Failure to observe the following precautions may result in system damage:
See Figure 1
To diagnose the ABS system or even a single component of the system, a scan tool (DRB, DRB II or equivalent) is necessary. Follow the on-screen instructions displayed on the scan tool. Because of the complexity of the ABS system and the importance of correct system functioning, it is a good idea to have a qualified automotive mechanic test the system if any problems have been detected.
The self-diagnostic ABS start up cycle begins when the ignition switch is turned to the ON position. An electrical check is completed on the ABS components, such as the wheel speed sensor continuity and other relay continuity. During this check the amber anti-lock light is turned on for approximately 1-2 seconds.
Further functional testing is accomplished once the vehicle is set in motion.
If the vehicle is not set in motion within 3 minutes from the time the ignition switch is set in the ON position, the solenoid test is bypassed, but the pump/motor is activated briefly to verify that it is operating correctly.
Fault codes are kept in a non-volatile memory until either erased by the DRB II or erased automatically after 50 ignition cycles (key ON-OFF cycles). The only fault that will not be erased after the 50 ignition cycles is the CAB fault. A CAB fault can only be erased by the DRB II. More than one fault can be stored at a time. The number of key cycles since the most recent fault was stored is also displayed. Most functions of the CAB and ABS system can be accessed by the DRB II for testing and diagnostic purposes.