ASC

DTC C1011 Abnormality in FL wheel speed sensor signal





CAUTION
^ If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines.
^ 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.

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.

DTC 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 DTC.
^ 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
^ ASC-ECU malfunction
^ Disturbance of magnetization pattern for wheel speed detection encoder
^ The number of poles on the Magnetic encoder for wheel speed detection (N-pole and S-pole) is changed

Past trouble
^ When DTC C100A 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.
^ When DTC C100A is not set, the following conditions may be present:
^ Some wheels slip
^ Unstable vehicle attitude
^ External noise interference
^ Vehicle ran with the parking brake applied

DIAGNOSIS

Required Special Tools:
^ MB991958: Scan Tool (M.U.T.-III Sub Assembly)
^ MB991824: Vehicle Communication Interface (V.C.I.)
^ MB991827: M.U.T.-III USB Cable
^ MB991910: M.U.T.-III Main Harness A
^ MB991997: ASC check harness

STEP 1. M.U.T.-III CAN bus diagnostics
Use scan tool to diagnose the CAN bus lines.

Q: Is the check result normal?
YES: Go to Step 3.
NO: Repair the CAN bus lines. On completion, go to Step 2.

STEP 2. DTC recheck after resetting CAN bus lines

Q: Is DTC C1011 set?
YES: Go to Step 3.
NO: The procedure is complete.

STEP 3. M.U.T.-III DTC
Check that DTC C100A is also set.

Q: Is DTC C100A also set?
YES: Perform the diagnosis for DTC C100A.
NO: Go to Step 4.

STEP 4. Check for wheel speed sensor installation
Check how the wheel speed sensor [FL] is installed (Disconnection of wheel speed sensor, loose mounting bolt, etc.).

Q: Is the check result normal?
YES: Go to Step 5.
NO: Reinstall the wheel speed sensor [FL] correctly. Then go to Step 16.

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

Q: Is the check result normal?
YES: Go to Step 6.
NO: Replace the wheel speed sensor [FL]. Then go to Step 16.

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 [FL] for looseness.

Q: Is the check result normal?
YES: Go to Step 7.
NO: Replace the wheel bearing.

STEP 7. Check of wheel speed detection encoder





Check the encoder for adhesion of foreign materials or deformation.

Q: Is the check result normal?
YES: 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.

STEP 8. Voltage measurement at the A-51 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.45 and the body ground and between the ground terminal No.46 and the body ground.
OK: 1 V or less

Q: Is the check result normal?
YES: Go to Step 9.
NO (Not normal at the terminal No.45 or 46): Go to Step 10.

STEP 9. Resistance measurement at A-51 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.45 and the body ground and between the ground terminal No.46 and the body ground.
OK: No continuity

Q: Is the check result normal?
YES: Go to Step 12.
NO (Not normal at the terminal No.45 or 46): Go to Step 10.

STEP 10. Connector check: A-51 ASC-ECU connector, A-07 wheel speed sensor [FL] connector

Q: Is the check result normal?
YES: Go to Step 11.
NO: Repair the defective connector. Then go to Step 16.

STEP 11. Wiring harness check between A-51 ASC-ECU connector terminal No.45 and A-07 wheel speed sensor [FL] connector terminal No.1 and between A-51 ASC-ECU connector terminal No.46 and A-07 wheel speed sensor [FL] connector terminal No.2.
^ Check for short circuit in wheel speed sensor [FL] circuit.

Q: Is the check result normal?
YES: Replace the wheel speed sensor [FL]. Then go to Step 16.
NO: Repair the wiring harness. Then go to Step 16.

STEP 12. Voltage measurement at the A-51 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.45 and the body ground.
OK: Battery positive voltage

Q: Is the check result normal?
YES: Go to Step 13.
NO: Go to Step 15.

STEP 13. Connector check: A-51 ASC-ECU connector, A-07 wheel speed sensor [FL] connector

Q: Is the check result normal?
YES: Go to Step 14.
NO: Repair the defective connector. Then go to Step 16.

STEP 14. Wiring harness check between A-51 ASC-ECU connector terminal No.45 and A-07 wheel speed sensor [FL] connector terminal No.1 and between A-51 ASC-ECU connector terminal No.46 and A-07 wheel speed sensor [FL] connector terminal No.2.
^ Check for open circuit in wheel speed sensor [FL] circuit.

Q: Is the check result normal?
YES: Go to Step 15.
NO: Repair the wiring harness. Then go to Step 16.

STEP 15. Check whether the DTC is reset.
1) Erase the DTC.
2) Drive the vehicle at 12 mph (20 km/h) or more.

NOTE: The ABS warning light does not turn OFF in some cases unless the vehicle runs at 12 mph (20 km/h) or higher.

Q: Is DTC C1011 set?
YES: Replace the hydraulic unit (ASC-ECU). Then go to Step 16.
NO: Intermittent malfunction.

STEP 16. Check whether the DTC is reset.
1) Erase the DTC.
2) Drive the vehicle at 12 mph (20 km/h) or more.

NOTE: The ABS warning light does not turn OFF in some cases unless the vehicle runs at 12 mph (20 km/h) or higher.

Q: Is DTC C1011 set?
YES: Return to Step 1.
NO: The procedure is complete.