Mitsubishi Evolution X. Manual - part 795
DIAGNOSIS
TSB Revision
ACTIVE SKID CONTROL SYSTEM (ASC)
35C-187
DTC C121A: Abnormality in steering wheel sensor initialization
CAUTION
• If there is any problem in the CAN bus lines, an incor-
rect 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.
• When the steering wheel sensor is replaced, always
perform calibration to make ASC-ECU learn the neutral
point. (Refer to
.)
• When the hydraulic unit (integrated with ASC-ECU) is
replaced, after turning the ignition switch ON and OFF
(vehicle information from ETACS-ECU is registered),
always perform the calibration of steering wheel sen-
sor, G and yaw rate sensor, brake fluid pressure sen-
sor, cut valve, and inlet valve.(Refer to
, and
.)
.
CIRCUIT OPERATION
Steering wheel sensor stores the neutral position learned using
scan tool MB991958. When the neutral position has not been
learned, the steering wheel sensor outputs the signal indicating
that the learning has not been performed.
.
DTC SET CONDITIONS
This diagnostic trouble code is set when it is detected that the
steering wheel sensor has not learned the neutral position.
.
PROBABLE CAUSES
• Neutral position of steering wheel sensor not learned
• Steering wheel sensor malfunction
• ASC-ECU malfunction
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
STEP 1. Using scan tool MB991958, diagnose the CAN bus
lines.
Using scan tool MB991958, diagnose the CAN bus lines.
Q: Is the check result normal?
YES : Go to Step 3.
NO : Repair the CAN bus lines. (Refer to GROUP 54C
−
Troubleshooting
.) After repairing the CAN
bus line, go to Step 2.