C1257

Circuit Description
DTC C1257 identifies an ABS motor circuit that shorts to ground. The malfunction will cause one of the following conditions to occur:
^ The ABS motor will not be controlled at the commanded current rate.
^ The driver circuit will allow current directly to the ground.

Conditions for Setting the DTC
DTC C1257 can set anytime.
A malfunction exists if The 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 DTC stores.
^ The ABS disables.
^ The ABS warning indicator turns ON.
^ A rehome is commanded on the other two channels to ensure they are in the home position.

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 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 an intermittent malfunction:
^ Rubbed-through wire insulation
^ An internal motor short
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 switch 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 EBCM.








C1257 LF ABS Motor Circuit Shorted to Ground