DTC B1401: Driver's Air Bag Module (1st Squib) System Fault 2 (Open in the Squib Circuit), DTC B1481: Driver's Air Bag Module (2nd Squib) System Fault 2 (Open in the Squib Circuit): Diagnosis

Required Special Tools: 

• MB991958: Scan Tool (MUT-III Sub Assembly)
  • MB991824: Vehicle Communication Interface (V.C.I.)
  • MB991827: MUT-III USB Cable
  • MB991910: MUT-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  ."
      Fig 1: Connecting Special Tool MB991910 To Data Link Connector

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

   Check again if the DTC is set.

   Fig 2: Connecting Special Tool MB991910 To Data Link Connector

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   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 driver's air bag module. (Using scan tool MB991958, read the diagnostic trouble code.) 
   1. Disconnect the negative battery terminal.
   2. Slide the outer housing of the driver's air bag module connector C-305 in the arrow direction shown, and disconnect the connector.
      Fig 3: Disconnecting Driver's Air Bag Module Connector C-305

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   3. Connect special tool MB991865 to special tool MB991866.
      CAUTION: Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.
   4. Insert special tool MB991866 into clock spring side of driver's air bag module connector C-305 (terminal No.1 and 2 < 1st squib > or terminal No.3 and 4 < 2nd squib >) by backprobing.
      Fig 4: Inserting Special Tool MB991866 Into Clock Spring Side Of Driver's Air Bag Module Connector C-305

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   5. Connect the negative battery terminal.
      CAUTION: Always DTC B1481 is set when checking DTC B1401. This is because the second side terminal is isolated when checking it, DTC B1481 is set but this is not a fault. In addition, always DTC B1401 is set when checking DTC B1481 because the first side terminal is isolated.
   6. Erase the diagnostic trouble code memory, and check the diagnostic trouble code.

   Q: Is the checked DTC set? 

   • YES:  Go to Step 4.
   • NO:  Replace the driver's air bag module. (Refer to AIR BAG MODULES AND CLOCK SPRING  ). Then go to  Step 6.
4. STEP 4. Check the clock spring. (Using scan tool MB991958, read the diagnostic trouble code.) 
   1. Disconnect the negative battery terminal.
   2. Disconnect the clock spring connector C-307.
      Fig 5: Disconnecting Clock Spring Connector C-307

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   3. Connect special tool MB991865 to special tool MB991866.
      CAUTION: Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.
      Fig 6: Inserting Special Tool MB991866 Into Harness Side Of Clock Spring Connector C-307

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   4. Insert special tool MB991866 into harness side of clock spring connector C-307 (terminal No.14 and 13 < 1st squib > or terminal No.11 and 12 < 2nd squib >) by backprobing.
   5. Connect the negative battery terminal.
      CAUTION: Always DTC B1481 is set when checking DTC B1401. This is because the second side terminal is isolated when checking it, DTC B1481 is set but this is not a fault. In addition, always DTC B1401 is set when checking DTC B1481 because the first side terminal is isolated.
   6. Erase the diagnostic trouble code memory, and check the diagnostic trouble code.

   Q: Is the checked DTC set? 

   • YES:  Go to Step 5.
   • NO:  Replace the clock spring. (Refer to AIR BAG MODULES AND CLOCK SPRING  ). Then go to  Step 6.
5. STEP 5. Check the harness between the SRS-ECU connector C-26 (terminal No.36 and 37 < 1st squib > or terminal No. 33 and 34 < 2nd squib >) and the clock spring connector C-307 (terminal No.13 and 14 < 1st squib > or terminal No. 11 and 12 < 2nd squib >) for open circuit. 
   1. Disconnect SRS-ECU connector C-26 and clock spring connector C-307.
      Fig 7: Disconnecting SRS-ECU Connector C-26

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      Fig 8: Disconnecting Clock Spring Connector C-307

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      CAUTION: Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.
   2. Check for continuity between the following terminals. It should be less than 2 ohms.

      < 1st squib > 

      Fig 9: Checking Continuity Between SRS-ECU Connector C-26 And Clock Spring Connector C-307 (1st Squib)

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      • SRS-ECU connector C-26 (terminal No.36) and the clock spring connector C-307 (terminal No.13)
      • SRS-ECU connector C-26 (terminal No.37) and the clock spring connector C-307 (terminal No.14)

      < 2nd squib > 

      Fig 10: Checking Continuity Between SRS-ECU Connector C-26 And Clock Spring Connector C-307 (2Nd Squib)

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      • SRS-ECU connector C-26 (terminal No.33) and the clock spring connector C-307 (terminal No.11)
      • SRS-ECU connector C-26 (terminal No.34) and the clock spring connector C-307 (terminal No.12)

   Q: Does continuity exist? 

   • YES:  Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1401 < 1st squib > or B1481 < 2nd squib > set, replace the SRS CONTROL UNIT (SRS-ECU) . (Refer to SRS CONTROL UNIT (SRS-ECU)  ). Then go to Step 6.
   • NO:  Replace the harness wires between SRS-ECU connector C-26 and clock spring connector C-307. Then go to Step 6.
6. STEP 6. Recheck for diagnostic trouble code. 

   Check again if the DTC is set.

   Fig 11: Connecting Special Tool MB991910 To Data Link Connector

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   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 B1401 < 1st squib > or B1481 < 2nd squib > set? 

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