DTC B1031, B1032: Air Thermo Sensor System (Vehicles without A/C): Diagnosis

Required Special Tool: 

• 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

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? 

   • YES:  Go to Step 2.
   • NO:  Repair the CAN bus line. (Refer to DIAGNOSIS ).
     Fig 1: Connecting Special Tool MB991910 To Data Link Connector

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

   Recheck if the DTC is set.

   1. Erase the DTC.
   2. Turn the ignition switch to "ON" position.
   3. Check if the DTC is set.

   Q: Is the DTC set? 

   • YES:  Go to Step 3.
   • NO:  It can be assumed that this malfunction is intermittent. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS .
3. STEP 3. Check fin thermo sensor connector C-119 and heater controller assembly (A/C-ECU) C-61 for loose, corroded or damaged terminals, or terminals pushed back in the connector  .

   Q: Are fin thermo sensor connector C-119 and heater controller assembly (A/C-ECU) connector C-61 in good condition? 

   • YES:  Go to Step 4.
   • NO:  Repair or replace the connector. Refer to HARNESS CONNECTOR INSPECTION .
4. STEP 4. Check the wiring harness between heater controller assembly connector (A/C-ECU) C-61 (terminals 26 and 27) and fin thermo sensor connector C-119 (terminals 1 and 2)  .
   • Check the sensor signal line and ground line for open and short circuit.

   Q: Is the wiring harness between heater controller assembly (A/C-ECU) connector C-61 (terminals 26 and 27) and fin thermo sensor connector C-119 (terminals 1 and 2) in good condition? 

   • YES:  Go to Step 5.
   • NO:  Repair the wiring harness.
5. STEP 5. Check the fin thermo sensor  .

   Measure the resistance between connector terminals 1 and 2 under at least two different temperatures. The resistance values should generally match those in the graph.

   NOTE: The temperature at the check should not exceed the range in the graph.

   Q: Is the air thermo sensor in good condition? 

   • YES:  Replace the heater controller assembly (A/C-ECU). Then go to Step 6.
   • NO:  Replace the fin thermo sensor. Then go to Step 6.
6. STEP 6. Recheck for diagnostic trouble code  .

   Check again if the DTC is set.

   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 the DTC set? 

   • YES:  Return to  Step 1.
   • NO:  The procedure is complete.
     Fig 2: Fin Thermo Sensor Temperature Resistance Graph

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.