C1242

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CIRCUIT DESCRIPTION
DTC C1242 detects 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 to RUN 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.

If an ESB cannot hold a piston in the home position, the piston may be driven back when the brake pedal is applied. Then the brake pedal will drop.

CONDITIONS FOR SETTING THE DTC
DTC C1242 can set during initialization at the following speeds:
^ 0 km (0 mph) when the brake is off
^ 5 km (3 mph) when the brake is on

A malfunction exists if the EBCM/EBTCM detects that the ESB could not hold the piston in the home position.

DTC C1286 always sets with DTC C1242.

ACTION TAKEN WHEN THE DTC SETS
^ A malfunction Diagnostic Trouble Code (DTC) stores.
^ The ABS/ETS/TCS disables.
^ The amber ABS/ETS/TCS warning indicator(s) turn on.
^ The red BRAKE warning indicator turns on.

CONDITIONS FOR CLEARING THE DTC
^ The condition responsible for setting the DTC no longer exists and the Scan Tool Clear DTCs function is used.
^ 100 drive cycles pass with no DTC(s) detected.

DIAGNOSTIC AIDS
The following conditions may cause an intermittent malfunction if the conditions exist in a mechanical part of the system:
^ Sticking
^ Binding
^ Slipping

Use the enhanced diagnostic function of the Scan Tool in order to measure the frequency of the malfunction. Refer to the Scan Tool manual for the procedure.

Use the hydraulic control modulator test function of the Scan Tool in order to locate an intermittent.

Clear the DTCs after completing the diagnosis. Test drive the vehicle for three drive cycles in order to verify that the DTC does not reset. Use the following procedure in order to complete one drive cycle:
1. Start the vehicle.
2. Drive the vehicle over 16 km/h (10 mph).
3. Stop the vehicle.
4. Turn the ignition to the OFF position.

IMPORTANT: Zero the J 39200 test leads before making any resistance measurements. Refer to the J 39200 user's manual.