DTC C1242: Rear Left Abs Sensor Signal

DTC detecting condition: 

• A fault is detected if the time of decompression or hold exceeds the predetermined time.
• A fault is detected if noise of the wheel speed sensor signal is detected.
• A fault is detected if the wheel speed sensor signal is lost, or the wheel speed sensor signal continuously indicates significantly low speed by calculating the difference between maximum speed and minimum speed among the four wheels.
• A fault is detected if the wheel speed sensor signal continuously indicates excessively high or low speed.
• A fault is detected if the wheel speed sensor signal changes irregularly.
• A fault is detected if the wheel speed sensor signal drops cyclically.

Trouble symptom: 

• ABS does not operate.
• VDC does not operate.
• AVH does not function.
• EyeSight does not operate.

1. CHECK ABS WHEEL SPEED SENSOR AND FREEZE FRAME DATA USING SUBARU SELECT MONITOR  .
   1. Using the Subaru Select Monitor, check the freeze frame data when the DTC for [Brake Control] is detected. Refer to BRAKE CONTROL (DIAGNOSTICS)>Freeze Frame Data .
   2. Compare [FR Wheel Speed], [FL Wheel Speed], [RR Wheel Speed] and [RL Wheel Speed] to determine a sensor that is not indicating the same value.
   3. Using the Subaru Select Monitor, check [Data Monitor] of the wheel speed sensor that is not indicating the same value in [Brake Control]. Refer to BRAKE CONTROL (DIAGNOSTICS)>Data Monitor .

      Does the speed indicated on [Data Monitor] change in response to the speedometer reading during acceleration/deceleration when the steering wheel is in the straight-ahead position? And, are the values on the freeze frame data of the vehicle speed from the four wheels indicated as almost identical?

      Yes  : Go to  2.

      No  : Go to  7.

2. CHECK POOR CONTACT OF CONNECTOR  .
   1. Turn the ignition switch to OFF.
   2. Check for poor contact of the connector between VDCCM&H/U and ABS wheel speed sensor.

      Is there poor contact of connectors between VDCCM&H/U and ABS wheel speed sensor?

      Yes  : Repair the connector.

      No  : Go to  3.

3. CHECK CAUSE OF SIGNAL NOISE  .

   Make sure the radio wave devices and electronic components are installed correctly.

   Are the radio wave devices and electronic components installed correctly?

   Yes  : Go to  4.

   No  : Install the radio wave devices and electronic components properly.

4. CHECK CAUSE OF SIGNAL NOISE  .

   Check if the noise sources (such as an antenna) are installed near the sensor harness.

   Are noise sources installed?

   Yes  : Install the noise sources apart from sensor harness.

   No  : Go to  5.

5. CHECK VDCCM&H/U  .
   1. Connect all connectors.
   2. Using the Subaru Select Monitor, perform the clear memory of [Brake Control]. Refer to COMMON (DIAG)>CLEAR MEMORY .
   3. Execute the inspection mode. Refer to BRAKE CONTROL (DIAGNOSTICS)>Inspection Mode .
   4. Read the DTC of [Brake Control] using the Subaru Select Monitor. Refer to BRAKE CONTROL (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

      Is the same DTC displayed?

      Yes  : Replace the VDCCM&H/U. Refer to VEHICLE DYNAMICS CONTROL (VDC)>VDC CONTROL MODULE AND HYDRAULIC CONTROL UNIT (VDCCM&H/U) .

      No  : Go to  6.

6. CHECK DETECTION OF OTHER DTCS FOR VDC  .

   Read the DTC of [Brake Control] using the Subaru Select Monitor. Refer to BRAKE CONTROL (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

   Is any other DTC displayed?

   Yes  : Perform the diagnosis according to the DTC. Refer to BRAKE CONTROL (DIAGNOSTICS)>Diagnostic Trouble Code (DTC)>LIST .

   No  : Currently, it is normal. There may have been a temporary poor contact in the harness and connector or a temporary noise interference.

7. CHECK INSTALLATION OF ABS WHEEL SPEED SENSOR  .

   Are the ABS wheel speed sensor installation bolts tightened to 7.5 N.m (0.76 kgf-m, 5.5 ft-lb)?

   Yes  : Go to  8.

   No  : Tighten the ABS wheel speed sensor installation bolts.

8. CHECK ABS WHEEL SPEED SENSOR  .

   Check the ABS wheel speed sensor. Refer to VEHICLE DYNAMICS CONTROL (VDC)>Front ABS Wheel Speed Sensor>INSPECTION . Refer to VEHICLE DYNAMICS CONTROL (VDC)>Rear ABS Wheel Speed Sensor>INSPECTION .

   Is the check result OK?

   Yes  : Go to  10.

   No  : Go to  9.

9. CHECK ABS WHEEL SPEED SENSOR OR MAGNETIC ENCODER  .

   Are there foreign matters adhered to the tip of ABS wheel speed sensor or magnetic encoder? Or is there any breakage or damage?

   Yes  : Remove dirt thoroughly. Also replace the ABS wheel speed sensor or magnetic encoder as a unit with hub unit bearing if it is broken or damaged.

   No  : Go to  10.

10. CHECK CAUSE OF SIGNAL NOISE  .

    Make sure the radio wave devices and electronic components are installed correctly.

    Are the radio wave devices and electronic components installed correctly?

    Yes  : Go to  11.

    No  : Install the radio wave devices and electronic components properly.

11. CHECK CAUSE OF SIGNAL NOISE  .

    Check if the noise sources (such as an antenna) are installed near the sensor harness.

    Are noise sources installed?

    Yes  : Install the noise sources apart from sensor harness.

    No  : Go to  12.

12. CHECK VDCCM&H/U  .
    1. Connect all connectors.
    2. Using the Subaru Select Monitor, perform the clear memory of [Brake Control]. Refer to COMMON (DIAG)>CLEAR MEMORY .
    3. Execute the inspection mode. Refer to BRAKE CONTROL (DIAGNOSTICS)>Inspection Mode .
    4. Read the DTC of [Brake Control] using the Subaru Select Monitor. Refer to BRAKE CONTROL (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

       Is the same DTC displayed?

       Yes  : Go to  13.

       No  : Go to  14.

13. CHECK FREEZE FRAME DATA OF ABS WHEEL SPEED SENSOR USING SUBARU SELECT MONITOR  .
    1. Using the Subaru Select Monitor, select freeze frame data of [Brake Control]. Refer to BRAKE CONTROL (DIAGNOSTICS)>Freeze Frame Data .
    2. Read the ABS wheel speed sensor output.

       Is the ABS wheel speed sensor output different compared with other wheels?

       Yes  : Replace the ABS wheel speed sensor which has a difference. Refer to VEHICLE DYNAMICS CONTROL (VDC)>Front ABS Wheel Speed Sensor . Refer to VEHICLE DYNAMICS CONTROL (VDC)>Rear ABS Wheel Speed Sensor .

       No  : Replace the VDCCM&H/U. Refer to VEHICLE DYNAMICS CONTROL (VDC)>VDC CONTROL MODULE AND HYDRAULIC CONTROL UNIT (VDCCM&H/U) .

14. CHECK DETECTION OF OTHER DTCS FOR VDC  .

    Read the DTC of [Brake Control] using the Subaru Select Monitor. Refer to BRAKE CONTROL (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

    Is any other DTC displayed?

    Yes  : Perform the diagnosis according to the DTC. Refer to BRAKE CONTROL (DIAGNOSTICS)>Diagnostic Trouble Code (DTC)>LIST .

    No  : Currently, it is normal. There may have been a temporary poor contact in the harness and connector or a temporary noise interference.

    NOTE: Though the ABS warning light may remain on at this time, this is normal. Drive the vehicle at 40 km/h (25 MPH) or more in order to turn ABS warning light off. Be sure to drive the vehicle and check that the warning light goes off.