Diagnostic Procedure

STEP 1. Scan tool CAN bus diagnostics
Using scan tool MB991958, diagnose the CAN bus lines.

Q: Is the check result normal?
1. YES: Go to Step 3.
2. NO: Repair the CAN bus lines. (Refer to TROUBLESHOOTING .) After repairing the CAN bus line, go to STEP 2 below.
STEP 2. Check whether the DTC is reset.
Q: Is DTC No. C121A set?
1. YES: Go to STEP 3 below.
2. NO: This diagnosis is complete.
STEP 3. Steering wheel sensor calibration
Perform calibration of the steering wheel sensor. (Refer to ON-VEHICLE SERVICE .)

Q: Has the calibration succeeded?
1. YES: Go to STEP 4 below.
2. NO: Replace the steering wheel sensor. (Refer to STEERING WHEEL SENSOR .) Then, go to STEP 4 below.
STEP 4. Check whether the DTC is reset.
Q: Is DTC No. C121A set?
1. YES: Replace the AWC-ECU. (Refer to AWC-ECU .) Then, go to STEP 5 below.
2. NO: Intermittent malfunction. (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTION .)
STEP 5. Check whether the DTC is reset.
Q: Is DTC No. C121A set?
1. YES: Return to Step 1.
2. NO: This diagnosis is complete.