GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2000 🢒 Firefly (Canada) 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C1251 Rear ABS Motor Free Spins

Object Number: 234313 Size: SF
ABS Components
Cell 44: Wheel Speed Sensors and Motor Pack
Handling ESD Sensitive Parts Notice

Circuit Description

DTC C1251 detects a stripped nut or gear assembly during initialization. During the homing sequence, the piston should reach the top of the bore. Then the ABS motor stalls. If the ABS motor does not stall, the ABS motor must be spinning with little or no resistance. This indicates a nut/screw or gear malfunction.

Conditions for Setting the DTC
    • DTC C1251 can only set during initialization.
    • A malfunction exists if the feedback current is less than the command current for a specified period of time.
    • This DTC can be set during motor re-home.

Action Taken When the DTC Sets
    • A malfunction DTC stores. A corresponding DTC C1286 will also set.
    • The ABS disables.
    • The ABS warning indicator turns 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 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

An intermittent malfunction in this DTC may result from a mechanical part of the system that slips, such as a stripped gear or a backed off gear retaining nut.

Depending on the frequency of the malfunction, a physical inspection of the mechanical parts suspected of causing the malfunction may be necessary.

Test Description

  1. This test checks for motor movement by comparing the motor feedback current to the motor command current during application.

    2.

  2. This test checks for motor movement by comparing the motor feedback current to the motor command current during release.

    3.

  3. This test checks for piston movement.

    4.

  4. This test checks for excessive resistance in the rear motor high circuit.

    5.

  5. This test checks for excessive resistance in the rear motor low circuit.

    6.

  6. This test checks for the correct resistance value of the rear motor .

    7.

  7. This test checks for correct operation of the motor-pack assembly.

    8.

  8. This test checks for correct operation of the hydraulic modulator.

    9.

  9. This test determines if the malfunction is caused by the EBCM.

Step

Action

Values

Yes

No

Important: Before making resistance measurements, zero the J 39200 test leads. Refer to the J 39200 user's manual.

1

Was A Diagnostic System Check-ABS performed?

--

Go to Step 2

Go to Diagnostic System Check - ABS

2
  1. Turn the ignition switch to the ON position.

    2. Do not start the engine.

  2. Use the Scan Tool in order to read the DTCs.

Does DTC C1264 also set as a current DTC?

--

Go to DTC C1264 Rear ABS Motor Circuit Open

Go to Step 3

3

  1. Pump the brake pedal until it is firm in order to empty the brake-booster vacuum reservoir.
  2. Select Special Functions on the Scan Tool .
  3. Select the Manual Control function on the Scan Tool .
  4. Select the rear ABS Motor Apply function on the Scan Tool .
  5. Use the Scan Tool in order to apply the rear ABS motor.
  6. Observe the following currents:
    7. • The command current of the rear ABS motor
    • The feedback current of the rear ABS motor

Did the command current of the rear ABS motor and the feedback current of the rear ABS motor match the specified current?

10 A

Go to Step 4

Go to Step 6

4

  1. Raise and support the vehicle so that the rear wheels are approximately 6 inches off the floor. Refer to Lifting and Jacking the Vehicle in General Information.
  2. Turn the ignition switch to the ON position.
  3. Apply firm pressure to the brake pedal.
  4. Select Special Functions on the Scan Tool .
  5. Select Manual Control on the Scan Tool .
  6. Use the Scan Tool in order to Apply the rear ABS motor.
  7. Have an assistant try to spin the rear wheels by hand.

Could the assistant spin the rear wheels?

--

Go to Step 5

Go to Step 6

5

  1. Continue to apply firm pressure to the brake pedal.
  2. Select the rear ABS Apply function on the Scan Tool .
  3. Use the Scan Tool in order to apply the rear ABS motor.

Could the assistant spin the rear wheels?

--

Go to Step 22

Go to Step 6

6

  1. Select Special Functions on the Scan Tool .
  2. Use the Scan Tool in order to perform the Gear Tension Relief function.
  3. Turn the ignition switch to the OFF position.
  4. Disconnect the connector of the ABS brake motor-pack assembly.
  5. Disconnect the connector of the EBCM.
  6. Use the J 39200 in order to measure the resistance between the following connectors:
    7. 6.1. Connector terminal C of the ABS brake motor-pack assembly
    6.2. Connector terminal F of the EBCM

Is the resistance within the specified range?

0-2 ohms

Go to Step 7

Go to Step 15

7

Use the J 39200 in order to measure the resistance between the following connectors:

    • Connector terminal D of the ABS brake motor-pack assembly
    • Connector terminal E of the EBCM .

Is the resistance within the specified range?

0-2 ohms

Go to Step 8

Go to Step 16

8

Use the J 39200 in order to measure the resistance between the following connectors:

    • Connector terminal C of the ABS brake motor-pack assembly
    • Connector terminal D of the ABS brake motor-pack assembly

Is the resistance within the specified range?

0.2-1.5 ohms

Go to Step 9

Go to Step 17

9
  1. Remove the ABS brake modulator assembly from the vehicle. Refer to Brake Pressure Modulator Valve Assembly Replacement .
  2. Remove the gear cover of the ABS brake modulator. Refer to Modulator Gear Cover Replacement .
  3. Inspect for a stripped rear gear in the ABS brake motor-pack assembly .

    4. The ABS brake motor-pack assembly is the unit with the 3 small gears. The rear gear of the ABS brake motor-pack assembly is the middle gear when the ABS brake modulator is mounted in the vehicle.

Is the ABS brake motor rear gear stripped?

--

Go to Step 17

Go to Step 10

10

Inspect for a stripped rear gear in the ABS brake modulator.

The ABS brake modulator unit is the unit with the 3 large gears. The rear gear of the ABS brake modulator is the middle gear when the ABS brake modulator is mounted in the vehicle.

Is the rear gear of the ABS brake modulator stripped?

--

Go to Step 18

Go to Step 11

11

  1. Reconnect the connector of the ABS brake motor-pack assembly.
  2. Reconnect the of the EBCM.
  3. Carefully secure the ABS brake modulator in the vehicle.

    4. Secure the assembly in a position that permits observation of the gears.

  4. Turn the ignition switch to the ON position.

    5. Do not start the engine.

  5. Select the Manual Control function on the Scan Tool .
  6. Select the rear ABS Motor Apply function on the Scan Tool .
  7. Use the Scan Tool in order to apply the rear ABS motor while observing the rear gear set of the ABS brake modulator.

    8. The rear gear of the ABS brake modulator is the middle gear when the ABS brake modulator is mounted in the vehicle.

  8. Select the rear ABS Motor Release function on the Scan Tool .
  9. Use the Scan Tool in order to release the rear ABS motor while observing the rear gear set of the ABS brake modulator.
  10. Select the rear ABS Motor Apply function on the Scan Tool .
  11. Use the Scan Tool in order to apply the rear ABS motor while observing the rear gear set of the ABS brake modulator.

Does the rear gear set of the ABS brake modulator move at least 1 full revolution in both directions?

--

Go to Step 12

Go to Step 17

12

  1. Use the Scan Tool in order to perform the Gear Tension Relief function.
  2. Turn the ignition switch to the OFF position.
  3. Separate the ABS brake motor-pack assembly from the ABS brake modulator.
  4. Grasp the rear gear of the ABS brake modulator.
  5. Rotate the rear gear of the ABS brake modulator.

Does the rear gear of the ABS brake modulator rotate more than 3.5 complete turns from lock position to lock position?

--

Go to Step 19

Go to Step 13

13
  1. Disconnect the connector of the ABS brake motor-pack assembly.
  2. Disconnect the EBCM connector.
  3. Inspect the connectors for the following conditions:
    4. • Poor terminal contact
    • Corrosion

Do any of the terminals exhibit poor terminal contact or corrosion?

--

Go to Step 20

Go to Step 14

14

  1. Reinstall the gear cover of the ABS brake modulator.
  2. Reinstall the ABS brake modulator assembly in the vehicle.
  3. Reconnect the connector of the ABS brake motor-pack assembly.
  4. Reconnect the EBCM connector.
  5. Start the engine. Do not apply pressure to the brake pedal.
  6. Let the engine run for at least 10 seconds.
  7. Turn the ignition switch to the OFF position.
  8. Repeat the cycle in steps 5 through 7, 2 more times.
  9. Use the Scan Tool in order to read the DTCs.

Does DTC C1251 set as a current DTC?

--

Go to Step 21

Go to Step 22

15

Repair the high resistance in the PNK wire between the EBCM and the ABS motor-pack assembly. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

16

Repair the high resistance in the PNK/BLK wire between the EBCM and the ABS motor-pack assembly. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

17

Replace the ABS brake motor-pack assembly. Refer to ABS Motor Pack Replacement .

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

18

Replace the ABS brake modulator gear. Refer to Brake Modulator Gear Replacement .

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

19

Replace the ABS brake modulator. Refer to Brake Pressure Modulator Valve Assembly Replacement .

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

20

Replace the terminals that show signs of poor terminal contact or of corrosion. Refer to Connector Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

21

Replace the EBCM. Refer to Electronic Brake Control Module Replacement .

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

22

The malfunction is intermittent or is not present at this time.

Refer to Diagnostic Aids for more information.

Is the action complete?

--

System OK

--