C1251

DTC C1251: Rear ABS Motor Free Spins (Part 1 Of 2):

DTC C1251: Rear ABS Motor Free Spins (Part 2 Of 2):

DTC C1251 Schematic:

Circuit Description
This DTC is designed to detect a stripped ball screw or gear assembly during motor re-home. During the homing sequence, the piston should reach the top of the bore resulting in a stalled motor. If this does not occur, the motor must be spinning with little or no resistance, indicating a ball screw or gear malfunction.

Conditions for Setting the DTC
This DTC will set when the following conditions are met:
^ The Electronic Brake Control Module (EBCM) monitors the time in which the left front motor is commanded in the forward direction. If this time duration exceeds the hydraulic modulator total travel time, the left front motor is spinning freely (feedback current is less than 12A).
^ This DTC can be set during motor re-home.

Action Taken When the DTC Sets
A malfunction DTC is stored, ABS is disabled, and the amber ABS indicator lamp is turned ON.

Conditions for Clearing the DTC
^ Conditions for the malfunction are no longer present and the Tech 2 scan tool Clear DTC Information function is used.
^ One hundred drive cycles have passed with no malfunctions detected.

Diagnostic Aids
The following list contains items that need to be inspected when diagnosing this system:
^ Faulty motor pack.
^ Stripped gear/ball screw/shaft.
^ Faulty (open/high resistance) left front motor electrical circuits during an ABS event or initialization.
An intermittent malfunction in this DTC may result from a mechanical part of the system that slips.



Test Description
The numbers below refer to step numbers on the diagnostic table.
3. Checks for Rear motor movement.
4. Checks for Rear motor movement.
5. Checks for a stripped motor pack gear.
6. Checks for a stripped hydraulic modulator gear.
7. Checks for a stripped ball screw.
8. Checks if this DTC resets after two drive cycles.
14. Makes sure that motors are at home position after repairs.