DTC B1C39: Driver's Seat belt Pre-tensioner (Squib) System (Shorted to Squib Circuit Power Supply): 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)
• MB991865: Dummy resistor
• MB991884: Resister harness

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  ."
   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. 

   Check again if the DTC is set.

   1. Erase the DTC.
   2. Turn the ignition switch to "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:  Go to Step 3.
   • NO:  Go to  Step 6.
3. STEP 3. Check the driver's seat belt pre-tensioner. 
   1. Disconnect the negative battery terminal.
   2. Disconnect driver's seat belt pre-tensioner connector D-21. Use a flat-tipped screwdriver to unlock the locking button at the harness side connector by withdrawing it toward you in two stages, and then disconnect the connector.
      Fig 2: Disconnecting Driver'S Seat Belt Pre-Tensioner Connector

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   3. Connect special tool MB991865 to special tool MB991884.
   4. Connect special tool MB991884 to the D-21 harness side connector.
   5. Connect the negative battery terminal.
   6. Erase diagnostic trouble code memory, and check the diagnostic trouble code.

   Q: Is DTC B1C39 set? 

   • YES:  Go to Step 4.
   • NO:  Replace the driver's seat belt with pre-tensioner (Refer to SEAT BELTS WITH PRE-TENSIONER  ). Then go to  Step 6.
     Fig 3: Connecting Special Tool MB991884 To D-21 Harness Side Connector

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
4. STEP 4. Check the driver's seat belt pre-tensioner circuit. Measure the voltage at the SRS-ECU connector C-30. 
   1. Disconnect the negative battery terminal.
   2. While pushing the part "A" indicated in the illustration of the harness side connector, turn the lock lever to the direction of the arrow to release the lock lever, and disconnect the C-30 SRS-ECU connector.
      Fig 4: Turning Lock Lever

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      CAUTION: To prevent the seat belt pre-tensioner from deploying unintentionally, disconnect the driver's seat belt pre-tensioner connector D-21 to short the squib circuit.
   3. Disconnect driver's seat belt pre-tensioner connector D-21. Use a flat-tipped screwdriver to unlock the locking button at the harness side connector by withdrawing it toward you in two stages, and then disconnect the connector.
      Fig 5: Disconnecting Driver'S Seat Belt Pre-Tensioner Connector

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      CAUTION: Insert an insulator such as a cable tie to a depth of 4mm (0.16 inch) or more, otherwise the short spring will not be released.
   4. Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] between terminals 45, 46 and the short spring to release the short spring.
   5. Connect the negative battery terminal.
   6. Ignition switch: "ON".
      Fig 6: Inserting Cable Tie Wide Thick Between Terminals 45, 46 And Short Spring

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   7. Measure the voltage between C-30 harness side connector terminals 45, 46 and body ground. Voltage should measure 1 volt or less.

   Q: Is the measured voltage within the specified range? 

   • YES:  Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1C39 sets, replace the SRS-ECU (Refer to SRS CONTROL UNIT (SRS-ECU)  ). Then go to  Step 6.
   • NO:  Go to Step 5.
     Fig 7: Measuring Voltage Between C-30 Harness Side Connector Terminals 45, 46 And Body Ground

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
5. STEP 5. Check the harness wires for short circuit to power supply between SRS-ECU connector C-30 (terminal No. 45 and 46) and driver's seat belt pre-tensioner connector D-21 (terminal No. 1 and 2). 

   Q: Is the check result normal? 

   • YES:  Go to Step 6.
   • NO:  Repair the harness wires between SRS-ECU connector C-30 and driver's seat belt pre-tensioner connector D-21. Then go to Step 6.
6. STEP 6. Recheck for diagnostic trouble code. 

   Check again if the DTC is set.

   1. Erase the DTC.
   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 B1C39 set? 

   • YES:  Return to  Step 1.
   • NO:  The procedure is complete.