DTC 42

42 REAR EXPANSION SPRING BRAKE (ESB) WILL NOT HOLD MOTOR

DTC 42 Rear ESB Will Not Hold Motor:

DTC 42 Rear ABS Will Not Hold Motor:

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

DTC Will Set When:
DTC 42 can be set during initialization. If the EBCM detects that the ESB could not hold the piston in the home position, a malfunction exists. DTC 86 is always set with DTC 42.

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, the amber ABS and the red BRAKE warning lamps are turned "ON."

DTC Chart Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks the rear axle ESB. A broken or defective ESB would result in the rear axle pistons being backdriven by hydraulic pressure and wheel movement would result.
2. Ensures that the proper motor circuits are located in the proper connector cavities.
3. Checks for high resistance in the motor "HIGH" circuitry.
4. Checks for high resistance in the motor "LOW" circuitry.
5. Checks for proper resistance of the motor windings.
6. Checks for poor terminal contact or corrosion in the connectors.
7. Checks for a malfunctioning EBCM.

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 hydraulic control modulator test function of the Tech 1 may be used to locate an intermittent malfunction associated with the ESB.