Code No.B1402 Driver’s air bag module (squib) system (shorted to squib circuit earth)


caution If the diagnosis code B1402 is set to SRS-ECU, be sure to diagnose the CAN bus line.

OPERATION
Only when the frontal impact exceeding the threshold is simultaneously detected (turned ON) by the front impact sensor as well as by the analogue G-sensor in SRS-ECU, the electric current is supplied from SRS-ECU to the driver’s air bag module (squib).

TROUBLE JUDGEMENT
The code is set when the input terminal of SRS-ECU driver’s air bag module (squib) shorted to earth.

PROBABLE CAUSES

  • Damaged clock spring
  • Damaged wiring harness and connectors
  • Driver’s air bag module (squib) harness shorted to earth
  • Malfunction of SRS-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics.
Use M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?
Go to Step 2
Repair the CAN bus line (Refer to GROUP 54C - Troubleshooting ).

STEP 2. Check whether the diagnosis code is reset.
(1)Connect the negative battery terminal.
(2)After erasing the diagnosis code memory, check the diagnosis code again.
(3)Disconnect the negative battery terminal.

Q. Is the diagnosis code No. B1402 set?
Go to Step 3
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).

STEP 3. Diagnosis check by dummy resistor connection.
(1)Check that the negative battery terminal is disconnected. If the negative battery terminal is connected, disconnect it.

(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 dummy resistor (MB991865) to special tool resistor harness (MB991866).

(4)
caution Do not insert a probe directly into the terminal from the connector front side as the connector contact pressure may be weakened.
Insert the resistor harness probe (special tool) as shown.
(5)Connect the negative battery terminal.
(6)After erasing the diagnosis code memory, check the diagnosis code again.

Q. Is the diagnosis code No. B1402 set?

Go to Step 4

Replace the driver’s air bag module (Refer to ).

STEP 4. Diagnosis check by dummy resistor connection.
(1)Check that the negative battery terminal is disconnected. If the negative battery terminal is connected, disconnect it.
(2)Disconnect the clock spring connector.

(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991866).
(4)
caution Do not insert a probe directly into the terminal from the connector front side as the connector contact pressure may be weakened.
Insert the resistor harness probe from the back of clock spring harness side connector DQ1-, DQ1+ line.
(5)Connect the negative battery terminal.
(6)After erasing the diagnosis code memory, check the diagnosis code again.

Q. Is the diagnosis code No. B1402 set?

Go to Step 5

Replace the clock spring (Refer to ).

STEP 5. Resistance measurement at the SRS-ECU connector.
(1)Check that the negative battery terminal is disconnected. If the negative battery terminal is connected, disconnect it.

(2)While pushing the part "A" indicated in the figure of the harness side connector, turn the lock lever to the direction of the arrow to release the lock lever, and disconnect the SRS-ECU connector.
(3)
caution To release SRS-ECU connector short spring in the following operations, disconnect this clock spring connector, and keep the squib circuit shorted.
Disconnect the clock spring connector.

(4)
caution The short spring may not be released due to the insufficient insertion. Therefore, insert the insulator for 4 mm or more.
Insert the insulator (width: 3 mm, thickness: 0.5 mm) such as cable tie between the DQ1-, DQ1+ line, and then release the short spring.
(5)Take the measurements below at the SRS-ECU harness side connector.
Continuity between DQ1-, DQ1+ line and body earth
OK: No continuity

Q. Is the check result normal?

Go to Step 6

Repair the wiring harnesses DQ1-, DQ1+ line between the clock spring connector and the SRS-ECU connector.

STEP 6. Check whether the diagnosis code is reset.

Q. Is the diagnosis code No. B1402 set?
Replace SRS-ECU (Refer to ).
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).