Code No. C1027 Abnormality in RL 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 ).

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 signals from each wheel speed sensor while the vehicle is being driven. If any fault below is found in these sensor signals, ABS-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 wheel speed detection encoder
  • Adhesion of foreign materials on the wheel speed sensor
  • Adhesion of foreign materials on the wheel speed detection encoder
  • 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 wheel speed detection encoder
  • ABS-ECU malfunction
  • Disturbance of magnetisation pattern for wheel speed detection encoder
  • 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. C1020 is also set, 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 ).
  • When the diagnosis code No. C1020 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 the diagnosis code No. C1027 set?
Go to Step 3.
This diagnosis is complete.

STEP 3. M.U.T.-III diagnosis code
Check that the diagnosis code No. C1020 is also set.

Q. Is the diagnosis code No. C1020 also set?
Perform the diagnosis for the diagnosis code No. C1020 (Refer to ).
Go to Step 4.

STEP 4. Check for wheel speed sensor installation
Check how the wheel speed sensor <RL> 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 <RL> 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 <RL> (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 Rear wheel hub assembly <RL (2WD)> (Refer to GROUP 27A - On-vehicle Service ).
  • Check the wheel bearing <RL (4WD)> for looseness (Refer to GROUP 27B - On-vehicle Service ).

Q. Is the check result normal?
Go to Step 7.
NO (2WD) : Replace the rear wheel hub assembly (Refer to GROUP 27A - Rear axle hub assembly ).
NO (4WD) : Replace the wheel bearing (Refer to GROUP 27B - Rear 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 (2WD)> : Replace the rear wheel hub assembly (Refer to GROUP 27A - Rear axle hub assembly ).

NO <Deformation (4WD)> : Replace the wheel bearing (Refer to GROUP 27B - Rear axle hub assembly ).

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 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 9.

NO (Not normal at the terminal No.24 or 25) : Go to Step 10.

STEP 9. 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 the body earth, and between the wheel speed sensor earth terminal No.25 and the body earth.
OK: No continuity

Q. Is the check result normal?

Go to Step 12.

NO (Not normal at the terminal No.24 or 25) : Go to Step 10.

STEP 10. 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 11.
Repair the defective connector.

STEP 11. 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 12. 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 13.

Go to Step 15.

STEP 13. 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 14.
Repair the defective connector.

STEP 14. 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 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 the diagnosis code No. C1027 set?
Replace the ABS-ECU (Refer to ).
Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).