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DTC B1631: Driver's knee air bag module (squib) system (short circuit between squib circuit terminals)
 
 
cautionIf DTC B1631 is set in the SRS-ECU, always diagnose the CAN main bus line.
 
 
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 knee air bag module (squib).
 
 
TROUBLESHOOTING HINTS
  • Improper engaged connector or defective short spring*
  • Short circuit between the knee 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 is damaged or improperly engaged, the short spring may not be released when the connector is connected.
 
 
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. Connector check: SRS-ECU, knee air bag module.
(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. After disconnecting the SRS-ECU connector, connect it again.
(3) After disconnecting the knee air bag module harness side connector, connect the connector again. For the knee air bag module harness side connector disconnection, use the flat-tipped screwdriver to pull out the harness side connector locking button. After releasing the lock, disconnect the harness side connector.
(4) Connect the negative battery terminal.
(5) After erasing the DTC memory, check the DTC again.
(6) Disconnect the negative battery terminal.
Is DTC B1631 set?
Go to Step 4.
Replace the connector concerned.
 
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) Use the flat-tipped screwdriver to pull out the locking button of harness side connector. After releasing the lock, disconnect the knee air bag module harness side connector.
(3) Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991884).
(4) Connect the resistor harness to the knee air bag module harness side connector.
(5) Connect the negative battery terminal.
(6) After erasing the DTC memory, check the DTC again.
(7) Disconnect the negative battery terminal.
Is DTC B1631 set?
Go to Step 5.
Replace the driver’s knee air bag module (Refer to ).
 
STEP 5. Resistance check 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 SRS-ECU 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 harness side connector. After releasing the lock, disconnect the knee air bag module harness side connector.
(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 KDS-, KDS+ line and the short spring, and release the short spring.
(5) Take the measurements below at the SRS-ECU harness side connector.
  • Continuity between KDS-, KDS+ line
OK: No continuity
Is the check result normal?
Go to Step 6.
Repair the wiring harness KDS-, KDS+ line between the SRS-ECU connector and the knee air bag module 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 B1631 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 ).