DTC U1120: Bus Line (CAN-C) Low Input; DTC U1121: Bus Line (CAN-C) High Input: 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 (Vehicles with CAN communication system)

1. STEP 1. 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. Refer to "HOW TO CONNECT THE SCAN TOOL (M.U.T.-III)  ."
   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? 

   1. YES:  Go to Step 2.
   2. NO:  Repair the CAN bus line (Refer to DIAGNOSIS ).
   Fig 1: Connecting Scan Tool To Data Link Connector

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
2. STEP 2. Recheck for diagnostic trouble code. 

   Check again if the DTC is set to the ETACS-ECU.

   1. Erase the DTC.
   2. Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
   3. Check if DTC is set.
   4. Turn the ignition switch to the "LOCK" (OFF) position.

   Q: Is the DTC set? 

   1. YES:  Replace the ETACS-ECU.
   2. NO:  The diagnosis is complete.