ECM M/T or PCM A/T

DTC U1120: Failure information on ECM [M/T] or PCM [A/T] (related to engine)

CAUTION:
- If DTC U1120 is set in the combination meter, diagnose the CAN main bus line.
- If DTC U1120 has been set, SWS related DTC 021 is also set. After SWS has been diagnosed, don't forget to erase DTC 021.

CIRCUIT OPERATION
Some instruments of the combination meter are linked to the CAN bus line. Both the combination meter and the ECM [M/T] or PCM [A/T] have a terminator resistor.

DTC SET CONDITIONS
The combination meter communicates with the ECM [M/T] or PCM [A/T] via CAN bus line. If failure information is sent to the ECM [M/T] or PCM [A/T], DTC U1120 will be set.

TECHNICAL DESCRIPTION (COMMENT)

Current trouble
- The ECM [M/T] or PCM [A/T] or the combination meter may be defective.

Past trouble
- Carry out diagnosis with particular emphasis on connector(s) or wiring harness between the ECM [M/T] or PCM [A/T] and the combination meter.

TROUBLESHOOTING HINTS
- The wiring harness or connectors may have loose, corroded, or damaged terminals, or terminals pushed back in the connector
- Malfunction of ECM [M/T] or PCM [A/T]
- Malfunction of combination meter

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: 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 line.

Use scan tool MB991958 to diagnose the CAN bus lines.

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 "ON" position.
3. Diagnose the CAN bus line.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the check result satisfactory?

YES : Go to Step 2.

NO : Repair the CAN bus lines.

STEP 2. Using scan tool MB991958, read the MFI system diagnostic trouble code.

Check if an MFI system diagnostic trouble code is set.

1. Turn the ignition switch to "ON" position.
2. Read the diagnostic trouble code.
3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the DTC set?

YES : Diagnose the MFI system by referring to Diagnostic Trouble Code Chart [2.4L ENGINE] Diagnostic Trouble Code Descriptions or Diagnostic Trouble Code Chart [3.8L ENGINE]. Diagnostic Trouble Code Descriptions

NO : Go to Step 3.

STEP 3. Using scan tool MB991958, read the for any diagnostic trouble code.

1. Turn the ignition switch to the "ON" position.
2. Check if a diagnostic trouble code, which relates to CAN communication-linked systems below, is set.
- ETACS-ECU
- A/C-ECU

3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the DTC set?

YES : Go to Step 4.

NO : Go to Step 5.

STEP 4. Recheck for diagnostic trouble code.

When the ECM [M/T] or PCM [A/T] is replaced, register the encrypted code. Refer to Encrypted Code Registration Criteria Table and then check that the diagnostic trouble code is not reset.

1. Turn the ignition switch to "ON" position.
2. Erase the diagnostic trouble code.
3. Turn the ignition switch to the "LOCK" (OFF) position.
4. Turn the ignition switch to "ON" position.
5. Check if the diagnostic trouble code is set.
6. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the check result normally?

YES : The procedure is complete.

NO : Replace the combination meter.

STEP 5. Recheck for diagnostic trouble code.

Replace the combination meter, and then check that the diagnostic trouble code is not reset.