C1257

CIRCUIT DESCRIPTION
This Diagnostic Trouble Code (DTC) identifies a motor circuit that is shorted to ground. A motor shorted to ground will not allow controlled ABS operation.

CONDITIONS FOR SETTING THE DTC
^ Diagnostic Trouble Code (DTC) C1257 can set anytime.
^ A malfunction exists if the Electronic Brake Control Module (EBCM) detects an out of range voltage on either of the left front ABS motor circuits.
^ An out of range voltage on either circuit indicates one of the following conditions:
- A circuit shorts to ground.
- An ABS brake motor shorts internally.

ACTION TAKEN WHEN THE DTC SETS
^ A malfunction Diagnostic Trouble Code (DTC) stores.
^ The ABS disables.
^ The ABS warning indicator turns ON.

CONDITIONS FOR CLEARING THE DTC
^ The condition responsible for setting the Diagnostic Trouble Code (DTC) no longer exists and the Scan Tool Clear DTCs function is used.
^ 100 drive cycles pass with no DTCs detected. A drive cycle consists of starting the vehicle, driving the vehicle over 16 km/h (10 mph), stopping and then turning the ignition OFF.

DIAGNOSTIC AIDS
Use the Scan Tool Manual Control function in order to exercise ABS motor movement of affected channel in both directions while applying light pressure on the brake pedal. An intermittent malfunction may be indicated if erratic or jumpy brake pedal movement is detected while performing an apply or release function of the ABS monitor.
The following conditions may cause a malfunction:
^ Rubbed-through wire insulation
^ An internal motor short
^ Short to ground between the left front motor and the Electronic Brake Control Module (EBCM)
^ Left front motor armature winding grounded (low resistance to ground)

If the malfunction is not current, use the following procedure to pinpoint an intermittent malfunction in the motor circuitry or connections:
1. Wiggle the wires of the affected channel.
2. Inspect if the DTC resets.

Use the enhanced diagnostic function of the Scan Tool in order to measure the frequency of the malfunction.
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.

TEST DESCRIPTION
3. This test checks for a short to ground in the motor high circuit.
4. This test checks for a short to ground in the motor low circuit.
7. This test determines if the malfunction is caused by the Electronic Brake Control Module (EBCM).

Part 1 Of 2:

Part 2 Of 2:

DTC C1257 LF ABS MOTOR CIRCUIT SHORTED TO GROUND