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DTC B1631: Driver's Knee Air Bag (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 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 knee air bag module will deploy.
 
 
DTC SET CONDITIONS
This DTC is set if there is abnormal resistance between the input terminals of the knee air bag module (squib).
 
 
TROUBLESHOOTING HITS
  • Improper engaged connector or defective short spring*
  • Short circuit between the knee air bag module (squib) circuit terminals
  • Damaged connector(s)
note*: The squib circuit connectors integrate a "short" spring (which prevents the knee air bag module 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) (Refer to ). Therefore, if connector C-126 or C-223 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.
(1)
cautionTo prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
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 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 SRS-ECU connector C-126 and Knee air bag module connector C-223.
(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) Disconnect C-223 driver's knee air bag module harness side connector, and then reconnect it. Use a flat-tipped screwdriver to pull out the connector locking button toward the arrow direction, release the lock, and then disconnect the connector.
(4) Connect the negative battery terminal.
(5) Erase the diagnostic trouble code memory, and check the diagnostic trouble code.
Is DTC B1631 set?
Go to Step 4.
The procedure is complete. It is assumed that DTC B1631 set because connector C-126 or C-223 was engaged improperly.
 
STEP 4. Check the knee air bag module.
(1) Disconnect the negative battery terminal.
(2) Disconnect knee air bag module connector C-223. Use a flat-tipped screwdriver to unlock the locking button at the harness side connector by withdrawing it toward you in two stages, and then disconnect the connector.
(3) Connect special tool MB991865 to special tool MB991884.
(4) Connect the resistor harness to the C-223 harness side connector.
(5) Connect the negative battery terminal.
(6) Erase diagnostic trouble code memory, and then check the diagnostic trouble code.
Is DTC B1631 set?
Go to Step 5.
Replace the driver’s knee air bag module (Refer to . Then go to Step 7.
 
STEP 5. Check the knee air bag module circuit. Measure the resistance at the 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 knee air bag module from deploying unintentionally, disconnect the knee air bag module connector C-223 to short the squib circuit.
Disconnect knee air bag module connector C-223. Use a flat-tipped screwdriver to unlock the locking button at the harness side connector by withdrawing it toward you in two stages, 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 1, 2 and the short spring to release the short spring.
(5) Check for continuity between C-126 harness side connector terminals 1 and 2.It should be an open circuit.
Is it open circuit?
Erase the diagnostic trouble code memory, and check the diagnostic trouble code. If DTC B1631 sets, replace the SRS-ECU (Refer to ). Then go to Step 7.
Go to Step 6.
 
STEP 6. Check the harness for short circuit between SRS-ECU connector C-126 (terminal No.1 and 2) and knee air bag module connector C-223 (terminal No.1 and 2).
Is the check result normal?
Go to Step 7.
Repair the harness wires between SRS-ECU connector C-126 and knee air bag module connector C-223. Then go to Step 7.
 
STEP 7. 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 B1631 set?
Return to Step 1.
The procedure is complete.