DTC A051: Rear Motor Free Spins

REAR MOTOR FREE SPINS





Circuit Description
This DTC is designed to detect a stripped nut or gear assembly during initialization. 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. This indicates a nut/screw or gear malfunction.

Diagnosis
The system monitors the time in which the rear motor is commanded in the forward direction. If this time duration exceeds the modulator total travel time, the motor is spinning freely. The motor is considered moving if the sense current is less than 10.7 amps.

Cause(s)
- The gear, a nut, or a shaft is stripped.
- The gears or the shaft is dislocated.
- The motor pack assembly is faulty.
- There is a high resistance or an open circuit in the motor during ABS or initialization.

Fail Action
This is a critical operational fault. The ABS is disabled and the ABS warning lamp is turned on. The brake warning lamp is also turned on since this failure could cause degradation of the base brakes.

Test Description
The number(s) below refer to step(s) on the diagnostic table.
1. This step checks to see if the corresponding open ABS motor DTC is also set.
2. This step verifies that the ABS motor was actually applied as commanded by observing the feedback current.
3. This step verifies that the ABS motor can release.
4. This step verifies that the ABS motor can be applied by observing the pedal movement.
5. This test checks for high resistance in the rear ABS motor HIGH circuit.
7. This test checks for high resistance in the rear ABS; motor LOW circuit.
9. This test checks for proper resistance of the rear ABS motor winding.
12. This step checks for a stripped gear on the hydraulic modulator.

NOTICE: Be careful not to damage the gear set.

14. This test verifies that the rear ABS motor can be applied.
15. This verifies that the hydraulic modulator is functioning properly.
17. This ensures that the malfunction was not due to a poor terminal contact.

Diagnostic Aids
An intermittent malfunction in this DTC may result from a mechanical part of the system that sticks, binds, or slips.
Check the frequency of the malfunction by using the enhanced diagnostic feature of the scan tool as described in "Scan Tool Diagnostics." Scan Tool Diagnostics
If the DTC fails only once and DTC A064 also fails, refer to the table for DTC A064. If intermittent and enhanced diagnostics show this DTC fails during ABS operation, refer to the table for DTC A064.
Depending on the frequency of the malfunction, it may be necessary to perform a physical inspection of the mechanical parts suspected.
After all diagnosis is complete, clear the DTCs and test drive the vehicle for three drive cycles to verify that the DTC does not reset. A drive cycle consists of starting the vehicle, driving over 16 km/h (10 mph), and then turning off the ignition.











DTC A051 - Rear Motor Free Spins