A042

Diagnostic Chart:

Description:

CIRCUIT DESCRIPTION
This DTC is designed to detect a slipping rear axle Expansion Spring Brake (ESB). During initialization and braking, the rear motor is re-homed. If the ESB slips, the motor/piston will move. During the next key "ON" initialization, a re-home of the motor verifies the motor/piston remained at the home position. If motor movement is detected, the ESB must be slipping.

FAILURE CONDITION
DTC A042 cannot be set during initialization. If the Electronic Brake Control Module (EBCM) detects that the ESB could not hold the piston in the home position, a malfunction exists. DTC A086 is always set with DTC A042.

ACTION TAKEN
If an ESB cannot hold a piston in the home position, the piston may be backdriven when the brake pedal is applied, causing the brake pedal to drop. A malfunction DTC is stored, ABS is disabled, and the ABS indicator lamp and the red "BRAKE" warning lamp are turned "ON."

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step insures that the proper motor circuits are located in the proper connector cavities.
2. This step checks the rear axle ESB. A broken or defective ESB would result in the rear piston being backdriven by hydraulic pressure, and wheel movement would result.
3. This step performs the gear tension relief function to prepare the hydraulic modulator/motor pack assembly for separation.

DIAGNOSTIC AIDS
An "Intermittent" malfunction in this DTC may result from a mechanical part of the system that sticks, binds, or slips.

The frequency of the malfunction can be checked by using the enhanced diagnostic function of the Tech 1.

The static modulator test function of the Tech 1 or T-100 may be used to locate an intermittent malfunction associated with the ESB.