ANTI-LOCK BRAKE SYSTEM
(and HCU-Hydraulic Control Unit)
The 4-Wheel Anti-lock Brake System (ABS) is an electronically operated, all wheel brake control system. Major components include the power brake booster, master cylinder, the wheel speed sensors, and the Hydraulic Control Unit (HCU) which contains the control module, a relay, and the pressure control valves.
The system is designed to ****** wheel lockup during periods of high wheel slip when braking. Retarding wheel lockup is accomplished by modulating fluid pressure to the wheel brake units. When the control module detects a variation in voltage across the wheel speed sensors, the ABS is activated. The control module opens and closes various valves located inside the HCU. These valves, called dump and isolation valves, modulate the hydraulic pressure to the wheels by applying and venting the pressure to the brake fluid circuits.
Some models are equipped with a Traction Assist (TA) system. The TA system senses wheel spin upon acceleration, turns on the Hydraulic Control Unit (HCU) pump and applies fluid pressure to the appropriate rear wheel. Two additional isolation valves in the HCU will also close to permit fluid to flow only to the rear wheels.
The TA system monitors TA usage to avoid overheating the rear brakes. If the system does sense brake overheating, the ABS module will inhibit TA operation until the rear brakes are permitted to cool down.
The anti-lock brake system consists of the following components:
- Vacuum booster and master cylinder assembly
- Hydraulic Control Unit (HCU)
- ABS module
- Wheel sensors
- Pedal travel switch
On 1992-1994 and 1995-00 a scanner is used to perform the brake bleed. But on yours, I think it's different according to the manual.
What do you mean change the cal. on the rear also? Do you mean Caliper?