DTC B1731: Immobilizer Communication Failure: 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

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 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  2.

   NO:  Repair the CAN bus lines (Refer to PRECAUTIONS ON HOW TO REPAIR THE CAN BUS LINES ).

   Fig 1: Connecting Scan Tool To Data Link Connector

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

   Recheck if the diagnostic trouble code is set.

   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 diagnostic code set? 

   YES:  Replace the ECM < M/T> or the PCM < A/T>, and then record the VIN (Refer to ENCRYPTED CODE REGISTRATION CRITERIA TABLE ). Then go to Step  3.

   NO:  The procedure is complete.

   Fig 2: Connecting Scan Tool To Data Link Connector

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
3. STEP 3. Recheck for diagnostic trouble code. 

   Recheck if the diagnostic trouble code is set.

   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 diagnostic code set? 

   YES:  Replace the ETACS-ECU, and then record the VIN. Then, register the encrypted code again (Refer to ENCRYPTED CODE REGISTRATION CRITERIA TABLE ). Retest the system.

   NO:  The procedure is complete.

   Fig 3: Connecting Scan Tool To Data Link Connector

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.