DTC B1400: Driver's Air Bag Module (1st Squib) System Fault 1 (Short Circuit between Terminals of the Squib Circuit); DTC B1480: Driver's Air Bag Module (2nd Squib) System Fault 1 (Short Circuit between Terminals of the Squib Circuit): 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 Scan Tool To Data Link Connector

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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 MALFUNCTION ).

   Fig 2: Connecting Scan Tool To Data Link Connector

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3. STEP 3. Using scan tool MB991958, read the diagnostic trouble code. 
   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. Turn the ignition switch to the "ON" position.
   2. Check if the DTC is set.
   3. Turn the ignition switch to the "LOOK (OFF)" position.

   Q: Is DTC B1519 set? 

   YES  : Go to Step 4.

   NO  : Go to  Step 5.

   Fig 3: Connecting Scan Tool To Data Link Connector

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4. STEP 4. Check SRS-ECU connector C-26. 

   Q: Is the connector correctly engaged? 

   YES  : Go to Step 5.

   NO  : Engage the connector correctly. Then go to  Step 10.

   Fig 4: Identifying Connector C-26 Terminals

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5. STEP 5. Check SRS-ECU connector C-26, clock spring connector C-307 and driver's air bag module connector C-305. (Using scan tool MB991958, read the diagnostic trouble code.) 
   1. Disconnect the negative battery terminal.
   2. Disconnect connectors C-26, C-307 and C-305, 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 B1400 < 1st squib > or B1480 < 2nd squib > set? 

   YES  : Go to Step 6.

   NO  : The procedure is complete. It is assumed that DTC B1400 < 1st squib > or B1480 < 2nd squib > set because connector C-26, C-307 or C-305 was engaged improperly.

   Fig 5: Identifying Connector C-26 Terminals

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   Fig 6: Identifying Clock Spring Connector C-307 And Driver's Air Bag Module Connector C-305

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6. STEP 6. 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 clock spring side of driver's air bag module connector C-305 in the arrow direction shown, and disconnect the connector.
      Fig 7: Identifying Connector C-305 Terminals

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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. 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 No. 3 and 4 < 2nd squib >) by backprobing.
   5. Connect the negative battery terminal.
      Fig 8: Inserting Special Tool MB991866 Into Clock Spring Side Of Driver's Air Bag Module Connector C-305

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      CAUTION: Always DTC B1481 is set when checking DTC B1400. 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 B1480 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 7.

   NO  : Replace the driver's air bag module. (Refer to AIR BAG MODULES AND CLOCK SPRING  ). Then go to  Step 10.

7. STEP 7. 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 9: Identifying Connector C-307 Terminals

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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. Insert special tool MB991866 into clock spring harness side connector C-307 (terminal No. 13 and 14 < 1st squib > or No. 11 and 12 < 2nd squib >) by backprobing.
   5. Connect the negative battery terminal.
      Fig 10: Inserting Special Tool MB991866 Into Clock Spring Harness Side Connector C-307

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      CAUTION: Always DTC B1481 is set when checking DTC B1400. 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 B1480 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 8.

   NO  : Replace the clock spring. (Refer to AIR BAG MODULES AND CLOCK SPRING  ). Then go to  Step 10.

8. STEP 8. Check the driver's air bag module circuit. Measure the resistance at SRS-ECU connector C-26. 
   1. Disconnect SRS-ECU connector C-26.
      Fig 11: Identifying Connector C-26 Terminals

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      WARNING: To prevent the air bag from deploying unintentionally, disconnect clock spring connector C-307 to short the squib circuit.
   2. Disconnect clock spring connector C-307.
      Fig 12: Identifying Connector C-307 Terminals

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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.
   3. Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] between terminals 36, 37 < 1st squib > or 33, 34 < 2nd squib > and the short spring to release the short spring.
      Fig 13: Inserting Cable Tie Between Terminals 36, 37 (1st Squib) And Short Spring

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      Fig 14: Inserting Cable Tie Between Terminals 33, 34 (2nd Squib) And Short Spring

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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.
   4. Check for continuity between C-26 harness side connector terminals 36 and 37 < 1st squib > or 33 and 34 < 2nd squib >. It should be open circuit.

   Q: Does continuity exist? 

   YES  : Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1400 < 1st squib > or B1481 < 2nd squib > set, replace the SRS-ECU. (Refer to SRS CONTROL UNIT (SRS-ECU)  ). Then go to  Step 10.

   NO  : Go to Step 9.

   Fig 15: Checking Continuity Between C-26 Harness Side Connector Terminals 36 And 37 (1st Squib)

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   Fig 16: Checking Continuity Between C-26 Harness Side Connector Terminals 33 And 34 (2nd Squib)

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9. STEP 9. Check the harness for short circuit between SRS-ECU connector C-26 (terminal No. 36 and 37 < 1st squib > or No. 33 and 34 < 2nd squib >) and clock spring connector C-307 (terminal No. 13 and 14 < 1st squib > or No. 11 and 12 < 2nd squib >). 

   Q: Are harness wires between SRS-ECU connector C-26 (terminal No. 36 and 37 < 1st squib > or No. 33 and 34 < 2nd squib >) and clock spring connector C-307 (terminal No. 13 and 14 < 1st squib > or No. 11 and 12 < 2nd squib >) in good condition? 

   YES  : Go to Step 10.

   NO  : Replace the harness wires between SRS-ECU connector C-26 and clock spring connector C-307. Then go to Step 10.

   Fig 17: Identifying Connector C-26 Terminals

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   Fig 18: Identifying Connector C-307 Terminals

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10. STEP 10. 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 B1400 < 1st squib > or B1480 < 2nd squib > set? 

    YES  : Return to  Step 1.

    NO  : The procedure is complete.

    Fig 19: Connecting Scan Tool To Data Link Connector

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