Anti-Lock Brake System: Operation

The Teves Mark IVG Anti-Lock Brake System (ABS) ABS modulates brake fluid apply pressure during high pedal pressure and high vehicle deceleration to prevent wheel lock-up. Wheel lock-up does not mean wheel has stopped, but wheel is turning slower than other wheels.

Hydraulic Control Unit (HCU) consists of a valve body with a pump body, pump motor and accumulators attached. Accumulators store extra fluid released to system for ABS mode operation. Pump/motor provides fluid volume needed and is operated by a DC type motor. Pump/motor is controlled by Controller Anti-Lock Brake (CAB). Valve body contains CAB controlled solenoid valves that modulate brake pressure during ABS operation.

When ignition is switched on, CAB performs a static system initialization. When vehicle speed reaches approximately 6 MPH, CAB briefly cycles pump to verify operation. HCU solenoids are checked continuously. If a Diagnostic Trouble Code (DTC) is detected during system initialization, Amber ABS warning light will be activated and a DTC will be stored in CAB memory.

When ABS is activated, vibrations and/or pulsations may be felt in brake pedal. Pump/motor and solenoid valve cycling may be heard. Some wheel slip is required for best braking performance. This wheel slip may be heard as tire chirping. DO NOT  confuse tire chirping with tire skidding. Braking on rough road surfaces can cause wheel hop. CAB may detect wheel hop as a lock-up condition, causing ABS system to activate.