Code No. C1020 Abnormality in RL wheel speed sensor circuit
















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 ).

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 ABS-ECU. ABS-ECU uses the frequency of the pulse signals to determine the wheel speed.

DIAGNOSIS CODE SET CONDITIONS


ABS-ECU monitors the voltage fluctuation in each wheel speed sensor circuit. If ABS-ECU detects the open or short circuit in the circuit, it will set a diagnosis code.

PROBABLE CAUSES


Current trouble
  • Damaged wiring harness and connectors
  • Noise interference
  • Malfunction of wheel speed sensor
  • ABS-ECU malfunction
Past trouble
  • Carry out diagnosis with particular emphasis on wiring harness and connector failures between ABS-ECU and the wheel speed sensor. For diagnosis procedures, refer to How to treat past trouble (GROUP 00 - How to Use Troubleshooting/Inspection Service Points ).

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 the diagnosis code No. C1020 set?

Go to Step 3.
This diagnosis is complete.

STEP 3. M.U.T.-III data list


Check the following service data (Refer to ).

  • Item No.03: RL wheel speed sensor

Q. Is the check result normal?

Go to Step 12.
Go to Step 4.

STEP 4. Voltage measurement at the A-02 ABS-ECU connector



(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the voltage at the special tool connector side.
note Do not connect the special tool ABS check harness (MB991974) to ABS-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.24 and the body earth, and between the wheel speed sensor earth terminal No.25 and the body earth.
OK: 1 volt or less

Q. Is the check result normal?

Go to Step 5.

NO (Not normal at the terminal No.24 or 25) : Go to Step 6.

STEP 5. Resistance measurement at A-02 ABS-ECU connector



(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the harness-side connector, and then measure the resistance at the special tool connector side.
note Do not connect the special tool ABS check harness (MB991974) to ABS-ECU.
(2)Resistance between the wheel speed sensor power supply terminal (signal terminal) No.24 and body earth, and between the earth terminal No.25 and body earth.
OK: No continuity

Q. Is the check result normal?

Go to Step 8.

NO (Not normal at the terminal No.24 or 25) : Go to Step 6.

STEP 6. Connector check: A-02 ABS-ECU connector, C-131 intermediate connector, D-114 wheel speed sensor <RL> connector


Q. Is the check result normal?

Go to Step 7.
Repair the defective connector.

STEP 7. Wiring harness check between A-02 ABS-ECU connector terminal No.24 and D-114 wheel speed sensor <RL> connector terminal No.1, and between A-02 ABS-ECU connector terminal No.25 and D-114 wheel speed sensor <RL> connector terminal No.2



  • Check for short circuit in wheel speed sensor <RL> circuit

Q. Is the check result normal?

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

STEP 8. Voltage measurement at the A-02 ABS-ECU connector



(1)Disconnect the ABS-ECU connector, connect special tool ABS check harness (MB991974) to the ABS-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.24 and the body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 9.

Go to Step 11.

STEP 9. Wiring harness check between A-02 ABS-ECU connector terminal No.24 and D-114 wheel speed sensor <RL> connector terminal No.1, and between A-02 ABS-ECU connector terminal No.25 and D-114 wheel speed sensor <RL> connector terminal No.2.



  • Check for open circuit in wheel speed sensor <RL> circuit

Q. Is the check result normal?

Go to Step 10.
Repair the wiring harness.

STEP 10. Check for wheel speed sensor as a single unit


Refer to .

Q. Is the check result normal?

Go to Step 11.
Replace the wheel speed sensor <RL> (Refer to ).

STEP 11. Connector check: A-02 ABS-ECU connector


Q. Is the check result normal?

Go to Step 12.
Repair the defective connector.

STEP 12. 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 the diagnosis code No. C1020 set?

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