DTC B1401: Driver's Air Bag Module (1ST Squib) System (Squib Circuit Open); DTC B1481: Driver's Air Bag Module (2ND Squib) System (Squib Circuit Open): Diagnosis

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 .

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 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 .

1. Disconnect the negative battery terminal.
2. Use the flat-tipped screwdriver to pull out the locking button of wiring harness side connector, and release the lock.
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 1: Pulling Out Locking Button

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   Fig 2: Connecting Special Tool MB991865 To Special Tool MB991866

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4. Insert the resistor harness probe (special tool) as shown in the illustration.
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 DRIVER'S AIR BAG MODULE AND CLOCK SPRING  . Then go to Step  6.

1. Disconnect the negative battery terminal.
2. Disconnect the clock spring connector C-313.
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 resistor harness probe from the back of C-313 harness side connector (terminal No. 3 and 4 < 1st squib > or terminal No. 1 and 2 < 2nd squib >.
5. Connect the negative battery terminal.
   Fig 3: Connecting Special Tool MB991865 To Special Tool MB991866

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   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 DRIVER'S AIR BAG MODULE AND CLOCK SPRING  . Then go to Step  6.

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-126 SRS-ECU connector.
   Fig 4: Releasing Lock Lever

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   WARNING: To prevent the air bag from deploying unintentionally, disconnect the clock spring connector C-313 to short the squib circuit.
   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 5, 6 < 1st squib > or 3, 4 < 2nd squib > and the short spring to release the short spring.
   Fig 5: Identifying Cable Tie (1st Squib)

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   Fig 6: Identifying Cable Tie (2nd Squib)

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   CAUTION: Do not insert a probe into the terminal from C-313 harness side connector front side directly, as the connector contact pressure may be weakened.
4. Check for continuity between the following terminals. It should be less than 2 ohms.

   < 1st squib > 

   • SRS-ECU connector C-126 (terminal No. 5) and the clock spring connector C-313 (terminal No. 3)
   • SRS-ECU connector C-126 (terminal No. 6) and the clock spring connector C-313 (terminal No. 4)
     Fig 7: Checking Continuity Between SRS-ECU Connector C-126 Terminal No. 5 And Clock Spring Connector C-313 Terminal No. 3

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   < 2nd squib > 

   • SRS-ECU connector C-126 (terminal No. 3) and the clock spring connector C-313 (terminal No. 1)
   • SRS-ECU connector C-126 (terminal No. 4) and the clock spring connector C-313 (terminal No. 2)
     Fig 8: Checking Continuity Between SRS-ECU Connector C-126 Terminal No. 3 And Clock Spring Connector C-313 Terminal No. 1

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   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-ECU. (Refer to SRS CONTROL UNIT (SRS-ECU)  . Then go to Step 6.
   • NO:  Repair the harness wires between SRS-ECU connector C-126 and clock spring connector C-313 Then go to Step 6.

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 B1401 < 1st squib > or B1481 < 2nd squib > set? 

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