Code No. C101C Abnormality in FR wheel speed sensor signal












caution
  • If there is any problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to GROUP 54C, Trouble code diagnosis ).
  • Whenever ECU is replaced, ensure that the CAN bus lines are normal.
  • When the hydraulic unit (integrated with ASC-ECU) is replaced, always carry out the calibration of the steering wheel sensor, the G and yaw rate sensor and brake fluid pressure sensor (Refer to , and ).

OPERATION



  • The wheel speed sensor is a kind of a pulse generator. It consists of encoders (a plate on which north and south pole sides of the magnets are arranged alternately) for detecting the wheel speed which rotates at the same speed of the wheels and wheel speed sensors. This sensor outputs frequency pulse signals in proportion to the wheel speed.
  • The pulse signals, which the wheel speed sensor creates, are sent to ASC-ECU. ASC-ECU uses the frequency of the pulse signals to determine the wheel speed.

DIAGNOSIS CODE SET CONDITIONS


ASC-ECU monitors the signals from each wheel speed sensor while the vehicle is being driven. If any fault below is found in these sensor signals, ASC-ECU will set the relevant diagnosis code.

  • Irregular change in the wheel speed sensor signal
  • Wheel speed sensor signal continuously indicates high value.

PROBABLE CAUSES


Current trouble
  • Excessive gap between the wheel speed sensor and the magnetic encoder for wheel speed detection
  • Adhesion of foreign materials on the wheel speed sensor
  • Adhesion of foreign materials on the magnetic encoder for wheel speed detection
  • Wheel bearing malfunction
  • Malfunction of wheel speed sensor
  • Damaged wiring harness and connectors
  • External noise interference
  • Improper installation of the wheel speed sensor
  • Deformation of the magnetic encoder for wheel speed detection
  • ABS-ECU malfunction
  • Disturbance of magnetization pattern for magnetic encoder for wheel speed detection
  • The number of poles on the magnetic encoder for wheel speed detection (the number of N-pole and S-pole) is changed.
Past trouble
  • When the diagnosis code No. C1015 is also set, carry out diagnosis with particular emphasis on wiring harness and connector failures between ASC-ECU and the wheel speed sensor. For diagnosis procedures, refer to How to treat past trouble (GROUP 00 - How to Cope with Intermittent Malfunction ).
  • When diagnosis code No. C1015 is not set, the following conditions may be present:

    • Right or/and left wheels are rotated.
    • Unstable vehicle attitude
    • External noise interference
    • Vehicle ran with the parking brake applied.

DIAGNOSIS PROCEDURE


STEP 1. M.U.T.-III CAN bus diagnosis


Use M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?

Go to Step 3.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnosis table ). On completion, go to Step 2.

STEP 2. Diagnosis code recheck after resetting CAN bus lines


Q. Is diagnosis code No. C101C set?

Go to Step 3.
This diagnosis is complete.

STEP 3. M.U.T.-III diagnosis code


Check that the diagnosis code No. C1015 is also set.

Q. Is the diagnosis code No. C1015 also set?

Perform the diagnosis for the diagnosis code No. C1015 (Refer to ).
Go to Step 4.

STEP 4. Check for wheel speed sensor installation


Check how the wheel speed sensor <FR> is installed (Disconnection of wheel speed sensor, loose mounting bolt, etc.).

Q. Is the check result normal?

Go to Step 5.
Reinstall the wheel speed sensor <FR> correctly (Refer to ).

STEP 5. Check for wheel speed sensor as a single unit


Q. Is the check result normal?

Go to Step 6.
Replace the wheel speed sensor <FR> (Refer to ).

STEP 6. Check for wheel bearing looseness


note Loose wheel bearing may increase the gap between the wheel speed sensor and the wheel speed detection magnet encoder. Check the wheel bearing <FR> for looseness (Refer to GROUP 26 - On-vehicle Service ).

Q. Is the check result normal?

Go to Step 7.
Replace the wheel bearing (Refer to GROUP 26 - Front axle hub assembly ).

STEP 7. Check of wheel speed detection encoder



Check the encoder for adhesion of foreign materials or deformation.

Q. Is the check result normal?

Go to Step 8.

NO (Adhesion of foreign materials) : Remove the foreign materials and clean the encoder so as not to disturb the magnetization pattern on it while taking care of the magnet, magnetic substance, and magnetic attraction.

NO (Deformation) : Replace the wheel bearing (Refer to GROUP 26 - Front axle hub assembly ).

STEP 8. Voltage measurement at the A-03 ASC-ECU connector



(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the voltage at the special tool connector side.
note Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.
(2)Turn the ignition switch to the ON position.
(3)Measure the voltage between the wheel speed sensor power supply terminal (signal terminal) No.34 and the body earth, and between the wheel speed sensor earth terminal No.33 and the body earth.
OK: 1 volt or less

Q. Is the check result normal?

Go to Step 9.

NO (Not normal at the terminal No.34 or 33) : Go to Step 10.

STEP 9. Resistance measurement at A-03 ASC-ECU connector



(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the harness-side connector, and then measure the resistance at the special tool connector side.
note Do not connect the special tool ASC check harness (MB991997) to ASC-ECU.
(2)Resistance between the wheel speed sensor power supply terminal (signal terminal) No.34 and the body earth, and between the wheel speed sensor earth terminal No.33 and the body earth.
OK: No continuity

Q. Is the check result normal?

Go to Step 12.

NO (Not normal at the terminal No.34 or 33) : Go to Step 10.

STEP 10. Connector check: A-03 ASC-ECU connector, A-58 wheel speed sensor <FR> connector


Q. Is the check result normal?

Go to Step 11.
Repair the defective connector.

STEP 11. Wiring harness check between A-03 ASC-ECU connector terminal No.34 and A-58 wheel speed sensor <FR> connector terminal No.1, and between A-03 ASC-ECU connector terminal No.33 and A-58 wheel speed sensor <FR> connector terminal No.2.



  • Check for short circuit in the wheel speed sensor <FR> circuit.

Q. Is the check result normal?

Replace the wheel speed sensor <FR> (Refer to ).
Repair the wiring harness.

STEP 12. Voltage measurement at the A-03 ASC-ECU connector



(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to the ASC-ECU-side connector and harness-side connector, and then measure the voltage at the special tool connector side.
(2)Turn the ignition switch to the ON position.
(3)Measure the voltage between the wheel speed sensor circuit power supply terminal (signal terminal) No.34 and the body earth.
OK: Approximately battery voltage

Q. Is the check result normal?

Go to Step 13.

Go to Step 15.

STEP 13. Connector check: A-03 ASC-ECU connector, A-58 wheel speed sensor <FR> connector


Q. Is the check result normal?

Go to Step 14.
Repair the defective connector.

STEP 14. Wiring harness check between A-03 ASC-ECU connector terminal No.34 and A-58 wheel speed sensor <FR> connector terminal No.1, and between A-03 ASC-ECU connector terminal No.33 and A-58 wheel speed sensor <FR> connector terminal No.2.



  • Check for open circuit in the wheel speed sensor <FR> circuit.

Q. Is the check result normal?

Go to Step 15.
Repair the wiring harness.

STEP 15. Check whether the diagnosis code is reset.


(1)Erase the diagnosis code.
(2)Drive the vehicle at 20 km/h or more.
note The ABS warning lamp does not turn OFF in some cases unless the vehicle runs at 20 km/h or higher.

Q. Is diagnosis code No. C101C set?

Replace the ASC-ECU (Refer to ).
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).