System Operation

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Listed are some of the normal conditions which may exist during Anti-Lock Brake System (ABS) and Low Speed Traction Control System (LTCS) operation:

When ignition is turned on, brake pedal may drop and a popping sound may be heard. Brake pedal movement and popping sound are caused by pulsating of the valves in the HCU.
Brake pedal may pulsate during braking due to modulation of brake fluid pressure in each brake hydraulic circuit.
Clicking or buzzing sound may be heard with vehicle at approximately 7 MPH. Clicking or buzzing sound is caused by a system test which operates pump/motor to verify proper pump/motor operation.
Groaning sound may be heard at approximately 7 MPH while driving away from an ABS stop. Groaning sound may result if CAB has not completed a 500 millisecond pump/motor operation after the last pressure reduction and before reaching 2.5 MPH. Remainder of the 500 millisecond pump/motor operation must be completed at the next drive cycle when vehicle reaches 7 MPH.
Groaning sound may be heard during hard braking resulting in ABS operation. Groaning sound is caused by operation of valves in pump/motor to perform an ABS stop.
Brake pedal may ratchet downward at the end of an ABS stop. Brake pedal movement is caused by opening of inlet valves in the HCU to increase pressure in the brake hydraulic circuits.
On models with LTCS, a groaning sound may be heard when vehicle is accelerating until vehicle speed is approximately 30 MPH. Groaning sound may be caused by front wheel(s) slipping on the road surface and LTCS operating. The Green traction control function (TRAC CONT) light located on message center in instrument panel, will remain on until traction control cycle is completed.