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DTC B1400: Driver's Air Bag Module (1st squib) System (Short Circuit Between Squib Circuit Terminals)
DTC B1480: Driver's Air Bag Module (2nd squib) System (Short Circuit Between Squib Circuit Terminals)
 
 

caution
  • If DTC B1400 <1st squib> or B1480 <2nd squib> is stored in the SRS-ECU, always diagnose the CAN bus lines.
  • When DTC B1400 is stored in the following diagnosis, check the 1st squib circuit. When DTC B1480 is stored, 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 front air bag analog G-sensor. If the impact is over a predetermined level, the SRS-ECU sends an ignition signal. At this time, if the front air bag safing G-sensor is on, the SRS air bag will inflate.
  • The ignition signal is input to the air bag module via the clock spring to inflate the air bag.
 
 
DTC SET CONDITIONS
  • This DTC is stored if there is abnormal resistance between the input terminals of the driver's air bag module (squib). The most likely causes for this code to be stored are the followings:
    • Short circuit in driver’s air bag module (squib) or harness
    • Short circuit in the clock spring
 
 
TROUBLESHOOTING HINTS
  • Improper engaged connector or defective short spring*
  • Short circuit in the clock spring
  • Short circuit between the driver's air bag module (squib) circuit terminals
  • Damaged connector(s)
  • Malfunction of the SRS-ECU
note*: The squib circuit connectors integrate a "short" spring (which prevents the air bag from deploying unintentionally due to static electricity by shorting the positive wire to the ground wire in the squib circuit when the connectors are disconnected). Therefore, if connector C-126, C-303/C-316 or C-313 is damaged or improperly engaged, the short spring may not be released when the connector is connected.
 
 
DIAGNOSIS
STEP 1. Using scan tool MB991958, diagnose the CAN bus line.
cautionTo 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.
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 stored.
(1) Erase the DTC.
(2) Turn the ignition switch to "ON" position.
(3) Check if the DTC is stored.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC stored?
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 SRS-ECU connector C-126, driver’s air bag module connector C-303/C-316 and clock spring connector C-313.
(1) Disconnect the negative battery terminal.
(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. After disconnecting the C-126 SRS-ECU connector, connect it again.
(3) After disconnecting C-313 clock spring, connect it again.
(4) Disconnect the C-303/C-316 driver's air bag module connector using the flat-tipped screwdriver to pull out the locking button to the direction of the arrow, and connect it again.
(5) Connect the negative battery terminal.
(6) Erase the diagnostic trouble code memory, and check the diagnostic trouble code.
Is DTC B1400 <1st squib> or B1480 <2nd squib> stored?
Go to Step 4.
The procedure is complete. It is assumed that DTC B1400 <1st squib> or B1480 <2nd squib> is stored because connector C-126, C-303/C-316 or C-313 was engaged improperly.
 
STEP 4. Check the driver's air bag module.
(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.
(4)
cautionDo not insert a probe into the terminal from its front side directly as the connector contact pressure may be weakened.
Insert the resistor harness probe (special tool) as shown.
(5) Connect the negative battery terminal.
(6)
cautionAlways DTC B1481 is stored when checking DTC B1400. This is because the second side terminal is isolated when checking it. DTC B1481 is stored but this is not a fault. In addition, always DTC B1402 is stored when checking DTC B1480 because the first side terminal is isolated.
Erase the diagnostic trouble code memory, and check the diagnostic trouble code.
Is the checked DTC stored?
Go to Step 5.
Replace the driver's air bag module. (Refer to ). Then go to Step 8.
 
STEP 5. Check the clock spring.
(1) Disconnect the negative battery terminal.
(2) Disconnect the clock spring connector C-313.
(3) Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991866).
(4)
cautionDo not insert a probe into the terminal from C-313 harness side connector front side directly, as the connector contact pressure may be weakened.
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.
(6)
cautionAlways DTC B1481 is stored when checking DTC B1400. This is because the second side terminal is isolated when checking it. DTC B1481 is stored but this is not a fault. In addition, always DTC B1401 is stored when checking DTC B1480 because the first side terminal is isolated.
Erase the diagnostic trouble code memory, and check the diagnostic trouble code.
Is the checked DTC stored?
Go to Step 6.
Replace the clock spring. (Refer to ). Then go to Step 8.
 
STEP 6. Check the driver’s air bag module circuit. Measure the resistance at SRS-ECU connector C-126.
(1) Disconnect the negative battery terminal.
(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 C-126 SRS-ECU connector.

(3)
dangerTo prevent the air bag from deploying unintentionally, disconnect clock spring connector C-313 to short the squib circuit.
Disconnect clock spring connector C-313.
(4)
cautionInsert 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.
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.
(5) Check for continuity between C-126 harness side connector terminals 5 and 6 <1st squib> or 3 and 4 <2nd squib>.It should be open circuit.
Is it open circuit?
Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1400 <1st squib> or B1480 <2nd squib> is stored, replace the SRS-ECU. (Refer to ). Go to Step 8.
Go to Step 7.
 
STEP 7. Check the harness for short circuit between the harness wire and wire.
  • SRS-ECU connector C-126 (terminal No.5 and 6) and clock spring connector C-313 (terminal No.3 and 4) <1st squib>.
  • SRS-ECU connector C-126 (terminal No.3 and 4) and clock spring connector C-313 (terminal No.1 and 2) <2nd squib>.
the check result normal?
Go to Step 8.
Repair the harness wires between SRS-ECU connector C-126 and clock spring connector C-313. Then go to Step 8.
 
STEP 8. Recheck for diagnostic trouble code.
Check again if the DTC is stored.
(1) Erase the DTC.
(2) Turn the ignition switch to the "ON" position.
(3) Check if the DTC is stored.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is DTC B1400 <1st squib> or B1480 <2nd squib> stored?
Return to Step 1.
The procedure is complete.