Anti-Lock Brake System: Operation

The Teves Mark IVG Anti-Lock Brake System (ABS) is activated during hard braking to prevent wheel lock-up. Wheel lock-up does not mean wheel has stopped, but wheel is turning slower than vehicle speed.

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 provides the fluid volume needed and is operated by a DC type motor. Pump motor is controlled by ECU. Valve body contains ECU controlled solenoid valves that modulate brake pressure during ABS operation.

When ignition is on, before vehicle is moved, Electronic Control Unit (ECU) performs a static system initialization. When vehicle speed reaches approximately 6 MPH, ECU briefly cycles pump to verify operation. Hydraulic Control Unit (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 ECU.

When ABS is activated, vibrations and pulsations may be felt in brake pedal and solenoid valves clicking and pump motor running 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. When braking on rough road surfaces, ABS may activate, detecting wheel lock-up tendencies from wheel hop.