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DTC B1431: Side-airbag Module (LH) (Squib) System (Squib Circuit Open)
 
 

cautionIf DTC B1431 is set in the SRS-ECU, always diagnose the CAN bus lines.
 
 
CIRCUIT OPERATION
  • The SRS-ECU judges how severe a collision is by detecting signals from the side impact sensor installed on the lower side of the center pillar. If the impact is over a predetermined level, the SRS-ECU sends an ignition signal. At this time, if the side collision safing G-sensor is on, the SRS air bag will inflate.
  • The ignition signal is input to the side-airbag module to inflate the side-airbag.
 
 
DTC SET CONDITIONS
This DTC is set if there is abnormal resistance between the input terminals of the side-airbag module (LH) (squib).
 
 
TROUBLESHOOTING HINTS
  • Open circuit in the side-airbag module (squib) (LH) circuit
  • Improper connector contact
  • Malfunction of the SRS-ECU
 
 
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 "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the check result satisfactory?
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 "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. Check the side-airbag module (LH).
(1) Disconnect the negative battery terminal.
(2) Disconnect the D-32 side-airbag module connector, unlock the connector by sliding the locking button to the direction of the arrow as shown in the figure, and then disconnect the connector.
(3) Connect special tool MB991865 to special tool MB991866.
(4)
cautionDo not insert a test probe into the terminal from D-32 harness side connector front side directly, as the connector contact pressure may be weakened.
Insert special tool MB991866 into the D-32 harness side connector by backprobing.
(5) Connect the negative battery terminal.
(6) Erase diagnostic trouble code memory, and then check the diagnostic trouble code.
Is DTC B1431 set?
Go to Step 4.
Replace the front seatback assembly (Refer to ). Then go to Step 5.
 
STEP 4. Check the harness for open circuit between the SRS-ECU connector C-125 (terminal No. 39 and 40) and the side-airbag module (LH) connector D-32 (terminal No.2 and 1).
(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-125 SRS-ECU connector.

(3)
dangerTo prevent the air bag from deploying unintentionally, disconnect the side-airbag module (LH) connector D-32 to short the squib circuit.
Disconnect the D-32 side-airbag module connector, unlock the connector by sliding the locking button to the direction of the arrow as shown in the figure, and then disconnect the connector.
(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 39, 40 and the short spring to release the short spring.

(5)
cautionDo not insert a test probe into the terminal from D-32 harness side connector front side directly, as the connector contact pressure may be weakened.
Check for continuity between the following terminals. It should be less than 2 ohms.
  • SRS-ECU connector C-125 (terminal No.39) and the side-airbag module (LH) connector D-32 (terminal No.1)
  • SRS-ECU connector C-125 (terminal No.40) and the side-airbag module (LH) connector D-32 (terminal No.2)
Does continuity exist?
Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1431 sets, replace the SRS-ECU (Refer to ). Then go to Step 5.
Repair the harness wires between SRS-ECU connector C-125 and side-airbag module (LH) connector D-32. Then go to Step 5.
 
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 B1431 set?
Return to Step 1.
The procedure is complete.