Code No.B1631 Driver’s knee air bag module (squib) system (short circuit between squib circuit terminals)


caution If the diagnosis code B1631 is set to SRS-ECU, be sure to diagnose the CAN bus line.

OPERATION


Only when the frontal impact exceeding the threshold is simultaneously detected (turned ON) by the front impact sensor as well as by the analogue G-sensor in SRS-ECU, the electric current is supplied from SRS-ECU to the knee air bag module (squib).

TROUBLE JUDGEMENT


The code is set when the short circuit occurs to between the terminals of SRS-ECU knee air bag module (squib) circuit.

PROBABLE CAUSES



note *: The squib circuit connectors integrate a short spring (which prevents the air bags from being unintentionally deployed because of static electricity by shorting the positive wire to the earth wire in the squib circuit when the connectors are disconnected). Therefore, when the above codes are set, the short spring may not be released due to the damaged connector even when the connectors are connected.

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics.
Use M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C - Troubleshooting ).

STEP 2. Check whether the diagnosis code is reset.
(1)Connect the negative battery terminal.
(2)After erasing the diagnosis code memory, check the diagnosis code again.
(3)Disconnect the negative battery terminal.

Q. Is the diagnosis code No. B1631 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. 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 diagnosis code memory, check the diagnosis code again.
(6)Disconnect the negative battery terminal.

Q. Is the diagnosis code No. 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 diagnosis code memory, check the diagnosis code again.
(7)Disconnect the negative battery terminal.

Q. Is the diagnosis code No. 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)
danger To 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)
caution The short spring may not be released due to the insufficient insertion. Therefore, insert the insulator for 4 mm or more.
Insert an insulator (width: 3 mm, thickness: 0.5 mm) 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

Q. 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. Check whether the diagnosis code is reset.

Q. Is the diagnosis code No. 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 ).