ASC
DTC C102A: Mutual monitoring of RL wheel speed sensorCAUTION:
^ If there is any problem in the CAN bus lines, an incorrect diagnostic trouble code 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 diagnostic trouble code.
^ Missing wheel speed sensor signal
^ Wheel speed sensor signal continuously indicates low 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
^ Wheel bearing malfunction
^ Deformation of the wheel speed detection encoder
^ Adhesion of foreign materials on the wheel speed detection encoder
^ Malfunction of wheel speed sensor
^ Improper installation of the wheel speed sensor
^ ASC-ECU malfunction
^ The number of poles on the Magnetic encoder for wheel speed detection (N-pole and S-pole) is changed
Past trouble
^ When diagnostic trouble code C1020 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 diagnostic trouble code C1020 is not set, the following conditions may be present:
^ Some wheels slip
^ Rotate only two wheels with drum tester
^ 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
STEP 1. M.U.T.-III CAN bus diagnostics
Use M.U.T.-III 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. Diagnostic trouble code recheck after resetting CAN bus lines
Q: Is DTC C102A set?
YES: Go to Step 3.
NO: This diagnosis is complete.
STEP 3. M.U.T.-III diagnostic trouble code
Check that diagnostic trouble code C1020 is also set.
Q: Is DTC C1020 also set?
YES: Perform the diagnosis for DTC C1020. C1020
NO: 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?
YES: Go to Step 5.
NO: Reinstall the wheel speed sensor [RL] correctly.
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 [RL].
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 [RL] for looseness.
Q: Is the check result normal?
YES: Go to Step 7.
NO: Replace the Rear wheel 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?
YES: Go to Step 8.
NO: (Adhesion of foreign materials): Remove the foreign materials and clean the encoder so as not to disturb the magnetisation pattern on it while taking care of the magnet, magnetic substance, and magnetic attraction.
NO: (Deformation): Replace the Rear wheel hub assembly.
STEP 8. Check whether the diagnostic trouble code is reset.
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 C102A set?
YES: Replace the ASC-ECU.
NO: Intermittent malfunction.