Inspection Procedure 12: ABS/Skid Control/TCL Operates Too Frequently

Inspection Procedure 12: ABS/skid control/TCL operates too frequently.

CAUTION
^ 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 the ECU is replaced, ensure that the CAN bus lines are normal.

COMMENTS ON TROUBLE SYMPTOM
^ Although it is difficult to determine the trouble cause since it depends on the running status and road surface condition, a malfunction of hydraulic circuit may be present if no diagnostic trouble code is detected.
^ If a wheel or tire of other than the genuine specified size is mounted, the ABS/skid control/TCL may be activated prematurely.
^ If non-genuine braking device or non-genuine impact reducing device is mounted, the ABS/skid control/TCL may be activated prematurely.

PROBABLE CAUSES
^ Installation of wheel or tire other than genuine specified size
^ Tire pressure abnormality
^ Tire wear and deterioration
^ Installation of non-genuine braking device or non-genuine impact reducing device
^ Wheel alignment abnormality
^ Malfunction of brake-related components
^ Malfunction of wheel speed sensor
^ Malfunction of G and yaw rate sensor
^ Malfunction of steering wheel sensor
^ Malfunction of hydraulic unit (integrated with ASC-ECU)
^ Malfunction of hydraulic circuit
^ External noise interference

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
^ MB991997: ASC check harness

STEP 1. Check of wheels and tires
Perform the following checks.
^ Check of wheel and tire size
^ Tire wear and deterioration
^ Tire pressure check

NOTE: For the tire pressure, refer to the tire pressure label attached to the lower section of driver's side door striker.

Q: Is the check result normal?
YES: Go to Step 2.
NO: Correct the wheels and tires. Then go to Step 9.

STEP 2. Check the DTC.
Using scan tool, check the diagnostic trouble code for ASC system.

Q: Is the check result normal?
YES: Go to Step 3.
NO: Carry out the diagnosis for the DTC. Then go to Step 9.

STEP 3. Check of brake-related components other than hydraulic unit (integrated with ASC-ECU)
Perform the following checks, and also check that no non-genuine parts are installed.
^ Brake pad check
^ Brake disc runout check
^ Brake drag force check

Q: Is the check result normal?
YES: Go to Step 4.
NO: Repair or replace the trouble spot. Then go to Step 9.

STEP 4. Wheel alignment check
Perform the following checks, and also check that no non-genuine parts are installed.
^ Front wheel alignment check
^ Rear wheel alignment check

Q: Is the check result normal?
YES: Go to Step 5.
NO: Repair or replace the trouble spot. Then go to Step 9.

STEP 5. Check of wheel speed sensor
Check for the presence of non-genuine electronic components and wiring harness of non-genuine electronic components to near the wheel speed sensor (wheel speed detecting section and wiring harness section).

Q: Is the check result normal?
YES: Go to Step 6.
NO: Remove the non-genuine electronic components and wiring harness of non-genuine electronic components. Then go to Step 9.

STEP 6. Scan tool service data
Check the following service data.
^ Item 01: FL wheel speed sensor
^ Item 02: FR wheel speed sensor
^ Item 03: RL wheel speed sensor
^ Item 04: RR wheel speed sensor
^ Item 08: Lateral G sensor
^ Item 10: Master cylinder pressure
^ Item 11: Steering angle
^ Item 12: Yaw rate sensor
^ Item 129: FL wheel cylinder pressure
^ Item 130: FR wheel cylinder pressure
^ Item 131: RL wheel cylinder pressure
^ Item 132: RR wheel cylinder pressure

Q: Is the check result normal?
YES: Go to Step 7.
NO (Abnormality of items 01 to 04) : Check the installation status of corresponding wheel speed sensor.
NO (Abnormality of items 08, 12) : Check the installation status of G and yaw rate sensor.
NO (Abnormality of item 11) : Check the installation status of steering wheel sensor.
NO (Abnormality of items 10, 129 to 132) : Replace the hydraulic unit (incorporates in ASC-ECU).

STEP 7. Hydraulic unit check
Perform the following actuator tests, and check that the operation is normal.
^ Item 01: FL wheel ABS drive
^ Item 02: FR wheel ABS drive
^ Item 03: RL wheel ABS drive
^ Item 04: RR wheel ABS drive
^ Item 05: FL wheel TCL drive
^ Item 06: FR wheel TCL drive
^ Item 07: RL wheel TCL drive
^ Item 08: RR wheel TCL drive

Q: Is the check result normal?
YES: Go to Step 8.
NO: Replace the hydraulic unit (incorporates in ASC-ECU). Then go to Step 9.

STEP 8. Operation check of ABS/skid control/TCL

Q: Is the check result normal?
YES: Intermittent malfunction.
NO: Replace the hydraulic unit (incorporates in ASC-ECU). Then go to Step 9.

STEP 9. Operation check of ABS/skid control/TCL

Q: Is the check result normal?
YES: The procedure is complete.
NO: Return to Step 1.