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DTC B1412: Passenger's (front) air bag module (1st squib) system (shorted to squib circuit ground)
DTC B1492: Passenger's (front) air bag module (2nd squib) system (shorted to squib circuit ground)
 
 
caution
  • If DTC B1412 <1st squib> or B1492 <2nd squib> is set in the SRS-ECU, always diagnose the CAN main bus line.
  • When DTC B1412 is set in the following diagnosis, check the 1st squib circuit. When DTC B1492 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 analog 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 input to the air bag module to inflate the air bag.
 
 
DTC SET CONDITIONS
This DTC is set if there is abnormal resistance between the input terminals of the passenger's (front) air bag module (squib).
 
 
TROUBLESHOOTING HINTS
  • Damaged harness wires and connectors
  • Short to the ground in the passenger's (front) air bag module (squib) harness
  • Malfunction of the SRS-ECU
 
 
DIAGNOSIS
STEP 1. Using scan tool (M.U.T.-III), diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
Connect scan tool (M.U.T.-III). 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.
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 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.
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. 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)
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 ASQ+, ASQ- line <B1412>.
Insert the resistor harness probe from the back of harness side connector AQ2+, AQ2- line <B1492>.
(5) Connect the negative battery terminal.
(6)
cautionAlways DTC B1492 is set when checking DTC B1412. This is because the second side terminal is isolated when checking it. DTC B1492 is set but this is not a fault. In addition, always DTC B1412 is set when checking DTC B1492 because the first side terminal is isolated.
Erase the diagnostic trouble code memory, and check the diagnostic trouble code.
(7) Disconnect the negative battery terminal.
Is the checked DTC set?
Go to Step 4.
Replace the passenger's (front) air bag module (Refer to ).
 
STEP 4. 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)
dangerTo release the connector short spring in the following operations, disconnect this harness side connector, and keep the squib circuit shorted.
Use the flat-tipped screwdriver to pull out the locking button of wiring harness side connector, and release the lock.
(4)
cautionThe short spring may not be released due to the insufficient insertion. Therefore, insert the insulator for 4 mm (0.16 inch) or more.
Insert an insulator [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] such as cable tie between the ASQ+, ASQ- line, and then release the short spring.
(5) Take the measurements below at the harness side connector.
  • Continuity between ASQ+, ASQ- line and body ground <B1412>
OK: No continuity
  • Continuity between AQ2+, AQ2- line and body ground <B1492>
OK: No continuity
Is the check result normal?
Go to Step 5.
Repair ASQ+, ASQ- line <B1412> or AQ2+, AQ2- line <B1492> between the SRS-ECU connector and the passenger's (front) air bag module connector.
 
STEP 5. 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.
Is DTC B1412 (1st squib) or B1492 (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 ).