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.
• Hill start assist does not operate. (Models without EyeSight)
• AVH does not function. (Models with EyeSight)
• EyeSight does not operate. (Models with EyeSight)
  NOTE: This DTC may be stored when the wheel speed sensor connector is disconnected regardless of the ignition switch condition (ON/OFF). Perform the Clear Memory Mode after diagnosis if a DTC is recorded. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>CLEAR MEMORY MODE .

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 DTC is detected. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>SUBARU SELECT MONITOR>OPERATION>READ 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. Check the current data of the wheel speed sensor that is not indicating the same value. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>SUBARU SELECT MONITOR>OPERATION>READ CURRENT DATA .

   Does the speed indicated on the data monitor change in response to the speedometer reading during acceleration/deceleration when the steering wheel is in the straightahead position? In addition, are the wheel speeds of the freeze frame data for 4 wheels almost the same?

   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 VDC Control Module & H/U and ABS wheel speed sensor.

   Is there poor contact of connectors between VDC Control Module & 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 VDC CONTROL MODULE & H/U. 
   1. Connect all connectors.
   2. Perform the Clear Memory Mode. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>CLEAR MEMORY MODE .
   3. Perform the Inspection Mode. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>INSPECTION MODE .
   4. Read the DTC. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

   Is the same DTC displayed?

   Yes:  Replace the VDC Control Module & 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. 

   Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

   Is any other DTC displayed?

   Yes:  Perform the diagnosis according to DTC. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>LIST OF DIAGNOSTIC TROUBLE CODE (DTC) .

   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. 

   Is the ABS wheel speed sensor installation bolt 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 SIGNAL. 
   1. Prepare an oscilloscope.
   2. Check the ABS wheel speed sensor. Refer to VEHICLE DYNAMICS CONTROL (VDC)>FRONT ABS WHEEL SPEED SENSOR>INSPECTION>CHECK ABS WHEEL SPEED SENSOR UNIT . Refer to VEHICLE DYNAMICS CONTROL (VDC)>REAR ABS WHEEL SPEED SENSOR>INSPECTION>CHECK ABS WHEEL SPEED SENSOR UNIT .

   Does the oscilloscope indicate the waveform pattern like shown in the figure when the tire is slowly turned? Does the oscilloscope indication repeat the waveform pattern like shown in the figure when the tire is slowly turned in equal speed for one rotation or more?

   Yes:  Go to  10.

   No:  Go to  9.

9. CHECK ABS WHEEL SPEED SENSOR OR MAGNETIC ENCODER. 

   Are there foreign matter, breakage or damage at the tip of ABS wheel speed sensor or magnetic encoder?

   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 VDC CONTROL MODULE & H/U. 
    1. Connect all connectors.
    2. Perform the Clear Memory Mode. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>CLEAR MEMORY MODE .
    3. Perform the Inspection Mode. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>INSPECTION MODE .
    4. Read the DTC. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>READ 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". Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>SUBARU SELECT MONITOR>OPERATION>READ 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 VDC Control Module & 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. 

    Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>READ DIAGNOSTIC TROUBLE CODE (DTC) .

    Is any other DTC displayed?

    Yes:  Perform the diagnosis according to DTC. Refer to VEHICLE DYNAMICS CONTROL (VDC) (DIAGNOSTICS)>LIST OF DIAGNOSTIC TROUBLE CODE (DTC) .

    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.