DTC B1B12: Driver's Knee Air Bag (Squib) System (Squib Circuit Open): 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 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  : Go to Step 3.

   NO  : There is an intermittent malfunction such as poor engaged connector(s) or open circuit (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTION ).

3. STEP 3. Check the knee air bag module. 
   1. Disconnect the negative battery terminal.
   2. Disconnect knee air bag module connector C-39. 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: Identifying Knee Air Bag Module Connector C-39

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   3. Connect special tool MB991865 to special tool MB991884.
   4. Connect special tool MB991884 to the C-39 harness side connector.
   5. Connect the negative battery terminal.
   6. Erase diagnostic trouble code memory, and then check the diagnostic trouble code.

   Q: Is DTC B1B12 set? 

   YES  : Go to Step 4.

   NO  : Replace the driver's knee air bag module (Refer to KNEE AIR BAG MODULE  ). Then go to  Step 5.

   Fig 3: Connecting Special Tool MB991884 To C-39 Harness Side Connector

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
4. STEP 4. Check the harness for open circuit between SRS-ECU connector C-37 (terminal No. 1 and 2) and the knee air bag module C-39 (terminal No. 2 and 1). 
   1. Disconnect the negative battery terminal.
   2. While pushing the part "A" indicated in the figure of the harness side connector, turn the lock lever to the direction of the arrow to release the lock lever, and disconnect the C-37 SRS-ECU connector.
      Fig 4: Turning Lock Lever

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

      DANGER 

      To prevent the knee air bag module from deploying unintentionally, disconnect the knee air bag module connector C-39 to short the squib circuit. 

   3. Disconnect SRS-ECU connector C-37 and knee air bag module connector C-39, and measure at the wiring harness side. For connector C-39, 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: Identifying Knee Air Bag Module Connector C-39

      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 1, 2 and the short spring to release the short spring.
      Fig 6: Inserting Cable Tie Between Terminals

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   5. Connect C-39 harness side connector to special tool MB991884.
      Fig 7: Connecting C-39 Harness Side Connector To Special Tool MB991884

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   6. Check for continuity between the following terminals. It should be less than 2 ohms.
      • SRS-ECU connector C-37 (terminal No. 1) and the special tool (terminal No. 1)
      • SRS-ECU connector C-37 (terminal No. 2) and the special tool (terminal No. 2)
        Fig 8: Checking Continuity Between SRS-ECU Connector C-37 And Special Tool

        Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

   Q: Does continuity exist? 

   YES  : Erase the diagnostic trouble code memory, and recheck if any DTC set. If DTC B1B12 set, replace the SRS-ECU (Refer to SRS CONTROL UNIT (SRS-ECU)  ). Then go to Step 5.

   NO  : Replace harness wires between SRS-ECU connector C-37 and knee air bag module connector C-39. Then go to Step 5.

5. STEP 5. 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 B1B12 set? 

   YES  : Return to  Step 1.

   NO  : The procedure is complete.