Active Skid Control System (ASC)

DTC C1242: Abnormality in G and yaw rate sensor (longitudinal G sensor)

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.
^ Do not drop the G and yaw rate sensor or subject it to a shock.
^ When the G and yaw rate sensor is replaced, always perform the calibration to make ASC-ECU learn the neutral point.
^ When the hydraulic unit (integrated with ASC-ECU) is replaced, always perform the calibration of steering wheel sensor, G and yaw rate sensor, brake fluid pressure sensor, cut valve, and inlet valve.

CIRCUIT OPERATION
^ ASC-ECU supplies power to the G and yaw rate sensor at the terminal No. 1.
^ The G and yaw rate sensor outputs the signal to ASC-ECU via the special CAN bus lines.

DTC SET CONDITIONS
This diagnostic trouble code is set when an abnormality is detected by a comparison of the longitudinal G value output from G and yaw rate sensor with the wheel speed value output from wheel speed sensor.

PROBABLE CAUSES
^ Improper installation of the G and yaw rate sensor
^ G and yaw rate sensor malfunction
^ Wheel speed sensor malfunction
^ ASC-ECU malfunction
^ External noise interference

NOTE: This DTC may be set also when the vehicle is driven on the four-wheel drum tester.

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. 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 2.
NO: Repair the CAN bus lines. After repairing the CAN bus line, go to Step 2.

STEP 2. Check for diagnostic trouble codes of other systems
Check if diagnostic trouble code No. U0125 is also set in ASC-ECU.

Q: Is DTC U0125 set?
YES: Perform troubleshooting for the diagnostic trouble code that is set. Then go to Step 3.
NO: Go to Step 3.

STEP 3. Check whether the DTC is reset.

Q: Is DTC C1242 set?
YES: Go to Step 4.
NO: This diagnosis is complete.

STEP 4. Check of wheel speed sensor-related diagnostic trouble code
Using scan tool MB991958, check if the wheel speed sensor-related diagnostic trouble code is set.

Q: Is any DTC set?
YES: Perform troubleshooting for the diagnostic trouble code that is set.
NO: Go to Step 5.

STEP 5. G and yaw rate sensor check
Check that the G and yaw rate sensor is installed correctly.

Q: Is the check result normal?
YES: After checking the G and yaw rate sensor, perform the calibration of the G and yaw rate sensor to make ASC-ECU relearn the neutral point. Then go to Step 6.
NO: Reinstall the G and yaw rate sensor correctly. Then go to Step 8.

STEP 6. Scan tool service data
Check the following service data.
^ Item 09: G sensor

Q: Is the check result normal?
YES: Go to Step 7.
NO: Replace the G and yaw rate sensor. Then go to Step 7.

STEP 7. Check whether the DTC is reset.

Q: Is DTC C1242 set?
YES: Replace the hydraulic unit (incorporates in ASC-ECU). Then go to Step 8.
NO: Intermittent malfunction.

STEP 8. Check whether the DTC is reset.

Q: Is DTC C1242 set?
YES: Return to Step 1.
NO: The procedure is complete.