TCS or ASC

DTC U1120: CAN Communications System TCL Uncontrollable by Engine Malfunction

CAUTION
^ If DTC U1120 is set in the TCL/ASC-ECU, always diagnose the CAN main bus line. If there is any fault in the CAN bus lines, an incorrect DTC may be set.
^ Whenever the TCL/ASC-ECU is replaced, ensure that the communication circuit is normal.
^ The engine control system-related DTC may be set when DTC U1120 is set. Diagnose the engine control system first when the engine control system-related DTC is set.

DTC SET CONDITION
The TCL/ASC-ECU receives engine system-related signals from the ECM [M/T] or PCM [A/T] via CAN bus lines. If a fail-safe related data is contained in the signal from the ECM [M/T] or PCM [A/T], DTC
U1120 will be stored.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THESE DTCS ARE TO SET ARE:)
^ Damaged harness or connector.
^ Malfunction of the ECM [M/T] or PCM [A/T].
^ Malfunction of the TCL/ASC-ECU.

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, read the diagnostic trouble code.

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) Check for MFI system diagnostic trouble code.
4) Turn the ignition switch to the "LOCK" (OFF) position.
5) Disconnect scan tool MB991958,
Q: Is any DTC set?
YES: Repair the MFI control system. Then go to Step 6.
NO: Go to Step2.

STEP 2. Using scan tool MB991958, diagnose the 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 the CAN bus line.
4) Turn the ignition switch to the "LOCK" (OFF) position.
5) Disconnect scan tool MB991958.
Q: Is the CAN bus line found to be normal?
YES: Go to Step 3.
NO: Repair the CAN bus lines. Then go to Step 6.

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

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) Check if a DTC, which relates to CAN communication-linked systems below, is set.
A/C-ECU
^ DTC U1120: Failure Information on ECM [M/T] or PCM [A/T] (Related to engine).
4) Turn the ignition switch to the "LOCK" (OFF) position.
5) Disconnect scan tool MB991958.
Q: Is DTC U1120 set?
YES: Go to Step 4.
NO: Go to Step 5.

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

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) Use scan tool MB991958 to read the TCL/ASC diagnostic trouble codes.
4) Turn the ignition switch to the "LOCK" (OFF) position.
5) Disconnect scan tool MB991958.
Q: Is DTC U1120 set?
YES: Replace the ECM [M/T] or PCM [A/T]. Then go to Step 6.
NO: It can be assumed that this malfunction is intermittent.

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

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) Use scan tool MB991958 to read the TCL/ASC diagnostic trouble codes.
4) Turn the ignition switch to the "LOCK" (OFF) position.
5) Disconnect scan tool MB991958.
Q: Is DTC U1120 set?
YES: Replace the hydraulic unit (integrated with TCL/ASC-ECU). Then go to Step 6.
NO: It can be assumed that this malfunction is intermittent.

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

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) Use scan tool MB991958 to read the TCL/ASC diagnostic trouble codes.
4) Turn the ignition switch to the "LOCK" (OFF) position.
5) Disconnect scan tool MB991958.
Q: Is DTC U1120 set?
YES: Return to Step 1.
NO: The procedure is complete.