TCL

DTC U1120: CAN Communications System TCL Uncontrollable by Engine Malfunction

CAUTION:
^ If DTC U1120 is set in the ABS/TCL-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 ABS/TCL-ECU is replaced, ensure that the communication circuit is normal.
^ The engine control system-related DTC may be set when DTC U1120 is set. For details refer to Intersystem Affiliated DTC Reference Table. Diagnose the engine control system first when the engine control system-related DTC is set.

DTC SET CONDITION
The ABS/TCL-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 PCM, 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 ABS/TCL-ECU.

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, 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. Refer to MFI Diagnosis - Diagnostic Function - How to Read and Erase Diagnostic Trouble Code. Diagnostic Function
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is any DTC set?
YES: Repair the MFI control system. Refer to MFI Diagnosis - Diagnostic Trouble Code Chart. Then go to Step 6.
NO: Go to Step 2.

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.
Q: Is the CAN bus line found to be normal?
YES: Go to Step 3.
NO: Repair the CAN bus line, refer to Diagnosis. 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) Check if a DTC, which relates to CAN communication-linked systems below, is set.
^ DTC U1120: Failure Information on ECM [M/T] or PCM [A/T] (Related to Engine). Refer to Automatic A/C Diagnosis - Diagnostic Function - How to Read and Erase Diagnostic Trouble Code.

(3) Turn the ignition switch to the "LOCK" (OFF) position.
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) Check if the DTC is set.
(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]. [Refer to Engine Control Module (ECM) [M/T] or Powertrain Control Module (PCM) [A/T]]. Then go to Step 6.
NO: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction.

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) Check if the DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is DTC U1120 set?
YES: Replace the hydraulic unit (integrated with ABS/TCL-ECU). Then go to Step 6.
NO: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction.

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