DTC 24: Passenger's (Front) Air Bag Module (Squib) System Fault 1 (Short Circuit between Terminals of 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
  • MB991911: MUT-III Main Harness B (Vehicles without CAN communication system)
• MB991865: Dummy resister
• MB991866: Resister harness

1. STEP 1. Using scan tool MB991958, read the diagnostic trouble code. 

   Q: Is DTC 34 set? 

   • YES:  Go to Step 2.
   • NO:  Go to  Step 3.
     Fig 1: Connecting Special Tool MB991911 To Data Link Connector

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2. STEP 2. Check SRS-ECU connector C-12. 

   Q: Is the connector correctly engaged? 

   • YES:  Go to Step 3.
   • NO:  Engage the connector correctly. Then go to  Step 7.
     Fig 2: Identifying SRS-ECU Connector C-12

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3. STEP 3. Check SRS-ECU connector C-12 and passenger's air bag module connector C-106 (Using scan tool MB991958, read the diagnostic trouble code). 
   1. Disconnect the negative battery terminal.
   2. Disconnect connectors C-12 and C-106, and then reconnect them.
   3. Connect the negative battery terminal.
   4. Erase the diagnostic trouble code memory, and check the diagnostic trouble code.

   Q: Is DTC 24 set? 

   • YES:  Go to Step 4.
   • NO:  The procedure is complete. It is assumed that DTC 24 set as connector C-12 or C-106 was engaged improperly.
     Fig 3: Identifying Harness Connector C-12

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     Fig 4: Identifying Harness Connector C-106

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4. STEP 4. Check the passenger's air bag module (Using scan tool MB991958, read the diagnostic trouble code). 
   1. Disconnect the negative battery terminal.
   2. Unclip passenger's air bag module connector C-106.
      Fig 5: Identifying Air Bag Module Connector C-106

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   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. Disconnect the passenger's air bag module connector C-106, and insert special tool MB991866 into the harness connector by backprobing.
   5. Connect the negative battery terminal.
   6. Erase the diagnostic trouble code memory, and check the diagnostic trouble code.

   Q: Is DTC 24 set? 

   • YES:  Go to Step 5.
   • NO:  Replace the passenger's air bag module (Refer to AIR BAG MODULES AND CLOCK SPRING  .) Then go to  Step 7.
     Fig 6: Checking Harness Connector C-106

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5. STEP 5. Check the passenger's air bag module circuit at SRS-ECU connector C-12. 
   1. Disconnect SRS-ECU connector C-12.
      Fig 7: Identifying Harness SRS-ECU Connector C-12

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   2. Unclip passenger's air bag module connector C-106.

      DANGER 

      To prevents the air bag from deploying unintentionally, disconnect the passenger's air bag module connector C-106 to short the squib circuit. 

   3. Disconnect the passenger's air bag module connector C-106.
      Fig 8: Identifying Harness Air Bag Module Connector C-106

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      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 9, 10 and the short spring to release the short spring.
      Fig 9: Identifying Harness Connector C-12

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      CAUTION: Do not insert a test probe into the terminal from its front side directly as the connector contact pressure may be weakened.
   5. Check for continuity between C-12 harness connector terminals 9 and 10.

      It should be open circuit.

   Q: Does continuity exist? 

   • YES:  Go to Step 6.
   • NO:  Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC 24 sets, replace the SRS-ECU Refer to SRS CONTROL UNIT (SRS-ECU)  . Then go to  Step 7
     Fig 10: Checking Continuity Between C-12 Harness Connector Terminals 9 And 10

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6. STEP 6. Check the harness for short circuit between SRS-ECU connector C-12 (terminal No.9 and 10) and passenger's air bag module connector C-106 (terminal No.1 and 2.) 

   Q: Are harness wires between SRS-ECU connector C-12 (terminal No.9 and 10) and passenger's air bag module connector C-106 (terminal No.1 and 2) in good condition? 

   • YES:  Go to Step 7.
   • NO:  Repair the harness wires between SRS-ECU connector C-12 and passenger's air bag module connector C-106. Then go to Step 7.
     Fig 11: Identifying Harness SRS-ECU Connector C-12

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     Fig 12: Identifying Harness Air Bag Module Connector C-106

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7. STEP 7. Recheck for diagnostic trouble code. 

   Q: Is DTC 24 set? 

   • YES:  Return to  Step 1.
   • NO:  The procedure is complete (If no malfunctions are found in all steps, an intermittent malfunction is suspected. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTION .)