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DTC B1402: Driver's air bag module (1st squib) system (shorted to squib circuit ground)
DTC B1482: Driver's air bag module (2nd squib) system (shorted to squib circuit ground)
 
 
caution
  • If DTC B1402 (1st squib) or B1482 (2nd squib) is set in the SRS-ECU, always diagnose the CAN main bus line.
  • When DTC B1402 is set in the following diagnosis, check the 1st squib circuit. When DTC B1482 is set, check the 2nd squib circuit.
 
 
CIRCUIT OPERATION
  • The SRS-ECU judges how severe a collision is by detecting signals from the front impact sensors and the G-sensor in the SRS-ECU. If the impact is over a predetermined level, the SRS-ECU sends an ignition signal. At this time, the SRS air bag will inflate.
  • The ignition signal is sent to the air bag module via the clock spring to inflate the air bag.
 
 
DTC SET CONDITIONS
This DTC is set if there is abnormal resistance between the input terminals of the driver's air bag module (squib).
 
 
TROUBLESHOOTING HINTS
  • Malfunction of the clock spring
  • Damaged harness wires and connectors
  • Short to the ground in the driver's air bag module (squib) harness
  • Malfunction of the SRS-ECU
 
 
DIAGNOSIS
STEP 1. Using scan tool (M.U.T.-IIISE), diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn off the power supply mode of the electric motor switch before connecting or disconnecting scan tool (M.U.T.-IIISE).
Connect scan tool (M.U.T.-IIISE). Refer to "How to connect the scan tool ."
(2) Turn on the power supply mode of the electric motor switch.
(3) Diagnose the CAN bus line.
(4) Turn off the power supply mode of the electric motor switch.
Is the CAN bus line found to be normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C, Diagnosis ).
 
STEP 2. Recheck for DTC.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn on the power supply mode of the electric motor switch.
(3) Check if the DTC is set.
(4) Turn off the power supply mode of the electric motor switch.
Is the DTC set?
Go to Step 3.
There is an intermittent malfunction such as poor engaged connector(s) or open circuit (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).
 
STEP 3. Check the DTC by connecting a dummy resistor.
(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)
cautionDo 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 DTC memory, check the DTC again.
(7) Disconnect the negative battery terminal.
(8)
cautionAlways DTC B1482 is set when checking DTC B1402. This is because the second side terminal is isolated when checking it, DTC B1482 is set but this is not a fault. In addition, always DTC B1402 is set when checking DTC B1482 because the first side terminal is isolated.
Erase the DTC memory, and check the DTC.
Is the checked DTC 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)
cautionDo 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 harness side connector DQ1-, DQ1+ line <B1402>.
Insert the resistor harness probe from the back of harness side connector DQ2-, DQ2+ line <B1482>.
(5) Connect the negative battery terminal.
(6) After erasing the DTC memory, check the DTC again.
Is the checked DTC 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)
cautionTo 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)
cautionThe short spring may not be released due to the insufficient insertion. Therefore, insert the insulator for 4 mm (0.16 in) or more.
Insert the insulator [width: 3 mm (0.12 inch), thickness: 0.5 mm (0.02 inch)] such as cable tie between the DQ1-, DQ1+ line, and then release the short spring <B1402>.
Insert the insulator [width: 3 mm (0.12 inch), thickness: 0.5 mm (0.02 inch)] such as cable tie between the DQ2-, DQ2+ line, and then release the short spring <B1482>.

(5) Take the measurements below at the harness side connector.
  • Continuity between DQ1-, DQ1+ line and body ground <B1402>
OK: No continuity
  • Continuity between DQ2-, DQ2+ line and body ground <B1482>
OK: No continuity
Is the check result normal?
Go to Step 6.
Repair the wiring harnesses DQ1-, DQ1+ line <B1402> or DQ2-, DQ2+ line <B1482> between the clock spring connector and the SRS-ECU connector.
 
STEP 6. Recheck for DTC.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn on the power supply mode of the electric motor switch.
(3) Check if the DTC is set.
(4) Turn off the power supply mode of the electric motor switch.
Is DTC B1402 <1st squib> or B1482 <2nd squib> 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 ).