MFI

DTC U0121: ASC-ECU Time-out

CAUTION:
- If the ECM output the DTC U0121, make sure to diagnose the CAN bus line.
- Before replacing the ECU, make sure that the communication circuit is operating normally.

DESCRIPTIONS OF MONITOR METHODS
There is no data from ASC-ECU for the specified time. (ASC-ECU also detect communication error with ECM.)

MONITOR EXECUTION
Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
- Not applicable

Sensor (The sensor below is determined to be normal)
- Not applicable

DTC SET CONDITIONS

Logic Flow Chart

Logic Flow Chart:

Check Condition
- Battery positive voltage is between 10 and 16.5 volts.

Judgement Criterion
- Unable to receive ASC-ECU signals through the CAN bus line for 4 seconds.

COMMENT

Current Trouble
- Some of the possible causes are a harness or connector damage between the ECM and the ASC-ECU on the CAN bus line, a failure in the ASC-ECU power supply system, a failure in the ASC-ECU, or a failure in the ECM.

Past Trouble
- Proceed to troubleshoot based on a harness or connector damage on the CAN bus line between the ECM and ASC-ECU, and a failure in the ASC power supply system. Refer to "How to cope with past trouble"

NOTE:
- If a malfunction occurred in the past, a failure cannot be discovered through the MB991958 CAN bus diagnosis even if there might be a problem with the CAN bus.
- Furthermore, it is possible to narrow down the areas of the possible failures from the DTCs that are output by the ECUs, which are communicating on the CAN bus.

FAIL-SAFE AND BACKUP FUNCTION
- None

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- CAN line harness damage or connector damage.
- ASC-ECU failed.
- ECM failed.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A

STEP 1. Using scan tool MB991958, diagnose CAN bus line.







CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Diagnose CAN bus line.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the CAN bus line normal?

YES : Go to Step 2.

NO : Repair the CAN bus line. Then go to Step 6.

STEP 2. Using scan tool MB991958, read the diagnostic trouble code (DTC).

1. Turn the ignition switch to the "ON" position.
2. Read the ASC-ECU.
3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the ASC-DTC set?

YES : Refer to Active Stability Control System-Diagnostic Trouble Code Chart. Diagnostic Trouble Code Descriptions

NO : Go to Step 3.

STEP 3. Using scan tool MB991958, read the diagnostic trouble code (DTC).

1. Turn the ignition switch to the "ON" position.
2. Read the S-AWC-DTC, TC-SST-DTC, Shift lever-DTC and ETACS-DTC.
3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is DTCU0121 set?

YES : Go to Step 4.

NO : Go to Step 5.

STEP 4. Using scan tool MB991958, read the diagnostic trouble code (DTC).

1. Turn the ignition switch to the "ON" position.
2. After the MFI-DTC has been deleted, read the MFI-DTC again.
3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is DTCU0121 set?

YES : Replace the ASC-ECU. Then go to Step 6.

NO : It can be assumed that this malfunction is intermittent of CAN bus line between ECM and ASC-ECU.

STEP 5. Using scan tool MB991958, read the diagnostic trouble code (DTC).

1. Turn the ignition switch to the "ON" position.
2. After the MFI-DTC has been deleted, read the MFI-DTC again.
3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is DTCU0121 set?

YES : Replace the ECM. When the ECM is replaced, register the ID code. Then go to Step 6.

NO : It can be assumed that this malfunction is intermittent of CAN bus line between ECM and ASC-ECU.

STEP 6. Using scan tool MB991958, read the diagnostic trouble code (DTC).

1. Turn the ignition switch to the "ON" position.
2. After the MFI-DTC has been deleted, read the MFI-DTC again.
3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is DTCU0121 set?

YES : Retry the troubleshooting.

NO : The inspection is complete.