DTC B1B18: Curtain Air Bag Module (LH) (Squib) System (Shorted to Squib Circuit Ground): 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
• MB991866: 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:  There is an intermittent malfunction such as poor engaged connector(s) or open circuit (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS ).
3. STEP 3. Check by dummy resistor connection. 
   1. Disconnect the negative battery terminal.
   2. Disconnect the D-12 intermediate connector unlock the connector by sliding the locking button to the direction of the arrow as shown in the illustration , and then disconnect the connector.
      Fig 2: Disconnecting D-12 Intermediate Connector Unlock Connector

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   3. Connect special tool MB991865 to special tool MB991866.
      CAUTION: Do not insert a probe into the terminal from its front side directly, as the connector contact pressure may be weakened.
   4. Insert the probe of resistor harness, to which the dummy resistor is installed, from the back of D-12 intermediate connector (floor harness side).
   5. Connect the negative battery terminal.
   6. After erasing the diagnostic trouble code memory, check the diagnostic trouble code again.
   7. Disconnect the negative battery terminal.

   Q: Is DTC B1B18 set? 

   • YES:  Go to Step 4.
   • NO:  Go to  Step 5.
     Fig 3: Connecting Special Tool MB991865 To Special Tool MB991866

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
4. STEP 4. Resistance measurement at the C-30 SRS-ECU connector. 
   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.
      WARNING: To prevent the air bag from deploying unintentionally, disconnect the intermediate connector D-12 to short the squib circuit.
   3. Disconnect the D-12 intermediate connector unlock the connector by sliding the locking button to the direction of the arrow as shown in the illustration , and then disconnect the connector.
      Fig 5: Disconnecting D-12 Intermediate Connector Unlock Connector

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      CAUTION: The short spring may not be released due to the insufficient insertion. Therefore, insert the insulator for 4 mm (0.6 inch) or more.
   4. Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] between terminal 41, 42 and the short spring to release the short spring.
      Fig 6: Inserting Cable Tie Wide Thick Between Terminal 41, 42 And Short Spring

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   5. Check for continuity between C-30 wiring harness side connector terminal No. 41, 42 and body ground. It should be open circuit.

   Q: Is it open circuit? 

   • YES:  Go to  Step 6.
   • NO:  Repair the wiring harness.
     Fig 7: Checking Continuity Between C-30 Wiring Harness Side Connector Terminal 41, 42 And Body Ground

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
5. STEP 5. Resistance measurement at the D-12 intermediate connector. 
   1. Disconnect the negative battery terminal.
      WARNING: To prevent the air bag from deploying unintentionally, disconnect the curtain air bag module connector F-24 to short the squib circuit.
   2. Disconnect curtain air bag module (LH) F-24. 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 8: Disconnecting Curtain Air Bag Wiring Harness Connector

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   3. Disconnect the D-12 intermediate connector unlock the connector by sliding the locking button to the direction of the arrow as shown in the illustration , and then disconnect the connector.
      Fig 9: Disconnecting D-12 Intermediate Connector Unlock Connector

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   4. Because the short spring is installed to the D-12 intermediate connector (curtain air bag harness side), 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 10: Inserting Cable Tie Wide Thick Between Terminals 1, 2 And Short Spring

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      CAUTION: Do not insert a probe into the terminal from its front side directly as the connector contact pressure may be weakened.
   5. Check for continuity between the D-12 intermediate connector (module side) terminal No. 1, 2 and the body ground. It should be open circuit.

   Q: Is it open circuit? 

   • YES:  Replace the curtain air bag module (LH) (Refer to CURTAIN AIR BAG MODULE(S)  ).
   • NO:  Repair the wiring harness.
     Fig 11: Checking Continuity Between D-12 Intermediate Connector (Module Side) Terminal 1, 2 And Body Ground

     Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
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 B1B18 set? 

   • YES:  Replace SRS-ECU (Refer to SRS CONTROL UNIT (SRS-ECU)  ).
   • NO:  Intermittent Malfunction (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTION ).