DTC 25: Passenger's (Front) Air Bag Module (Squib) System Fault 2 (Open in the Squib Circuit): Diagnosis

Required Special Tools: 

• MB991958: Scan Tool (M.U.T.-III Sub Assembly)
  • MB991824: V.C.I.
  • MB991827: M.U.T.-III USB Cable
  • MB991911: M.U.T.-III Main Harness B
• MB991865: Dummy resister
• MB991866: Resister harness

1. STEP 1. Check the passenger's (front) air bag module (Using scan tool MB991958, read the diagnostic trouble code). 
   1. Disconnect the negative battery terminal.
   2. Disconnect passenger's (front) air bag module connector C-106.
      Fig 1: Disconnecting Passenger's (Front) 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 (front) 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 25 set? 

   YES:  Go to Step 2.

   NO:  Replace the passenger's (front) air bag module (Refer to AIR BAG MODULE(S) AND CLOCK SPRING  ). Then go to  Step 3.

   Fig 2: Inserting Special Tool Into Harness Connector

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2. STEP 2. Check the harness for open circuit between SRS-ECU connector C-12 (terminal No.9 and 10) and the passenger's (front) air bag module connector C-106 (terminal No.1 and 2). 
   1. Disconnect passenger's (front) air bag module connector C-106.
      Fig 3: Disconnecting Passenger's (Front) Air Bag Module Connector C-106

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   2. Disconnect SRS-ECU connector C-12.
      CAUTION: Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.
      Fig 4: Identifying Connector C-12 Terminals

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   3. Check for continuity between the following terminals. It should be less than 2 ohms.
      • SRS-ECU connector C-12 (terminal No.9) and the passenger's (front) air bag module connector C-106 (terminal No.2)
      • SRS-ECU connector C-12 (terminal No.10) and the passenger's (front) air bag module connector C-106 (terminal No.1)

   Q: Does continuity exist? 

   YES:  Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC 25 set, replace the SRS-ECU (Refer to SRS CONTROL UNIT (SRS-ECU)  ). Then go to Step 3.

   NO:  Repair the harness wires between SRS-ECU connector C-12 and passenger's (front) air bag module connector C-106. Then go to Step 3.

   Fig 5: Checking Continuity Between SRS-ECU Connector C-12 And Passenger's (Front) Air Bag Module Connector C-106

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3. STEP 3. Recheck the 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 25 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 ).

   Fig 6: Connecting Scan Tool To Data Link Connector

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