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DTC B1421: Side-airbag module (RH) (squib) system (open circuit of squib circuit)
 
 
cautionIf diagnostic trouble code B1421 is set in the SRS-ECU, be sure to diagnose the CAN bus line.
 
 
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 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 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 (RH) (squib).
 
 
TROUBLESHOOTING HINTS
  • Open circuit in the side-airbag module (RH) (squib) circuit
  • Improper connector contact
  • 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 "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.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
 
STEP 3. Check the side-airbag module (RH).
(1) Check that the negative battery terminal is disconnected. If the negative battery terminal is connected, disconnect it.
(2) Disconnect the side-airbag module (RH) 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 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 side-airbag module (RH) harness side connector.
(5) Connect the negative battery terminal.
(6) Erase the diagnostic trouble code memory, and check the diagnostic trouble code.
(7) Disconnect the negative battery terminal.
Is DTC B1421 set?
Go to Step 4.
Replace the front seatback pad and frame assembly (Refer to ).
 
STEP 4. Resistance measurement at the SRS-ECU connector and the side-airbag module (RH) 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 side-airbag module connector, and keep the squib circuit shorted.
Disconnect the side-airbag module (RH) 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)
cautionThe short spring may not be released due to the insufficient insertion, thus insert for 4 mm (0.16 inch) or more.
Insert the insulator [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] such as cable tie between the SRS+, SRS- line and the short spring, and then release the short spring.
(5)
cautionDo not insert a test probe directly into the terminal of side-airbag module (RH) harness side connector from the connector front side as the connector contact pressure may be weakened.
Take the measurements below at the SRS-ECU and side-airbag module (RH) harness side connectors.
  • Continuity SRS+ line between SRS-ECU connector and side-airbag module (RH) connector
  • Continuity SRS- line between SRS-ECU connector and side-airbag module (RH) connector
OK: Continuity (less than 2 Ω)
Is the check result normal?
Go to Step 5.
Repair the wiring harness SRS+, SRS- line between the side-airbag module (RH) connector and the SRS-ECU 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 B1421 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 ).