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 and safing 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

Damaged short spring ^*
Short circuit between terminals of knee air bag module (squib) circuit
Damaged connector(s)
Malfunction of SRS-ECU
Insufficient press of locking button or locking button not pressed

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: C-126 SRS-ECU, C-223 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 C-126 SRS-ECU connector, connect it again.

(3) After disconnecting the C-223 harness side connector, connect the connector again. For the C-223 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 C-223 harness side connector.

(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991884).
(4)Connect the resistor harness to the C-223 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 C-126 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 C-126 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 C-223 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 terminal 1/2 and the short spring, and release the short spring.
(5)Take the measurements below at the C-126 harness side connector.

Continuity between terminals 1 and 2

OK: No continuity

Q. Is the check result normal?

Go to Step 6.

Repair the wiring harness between the C-126 SRS-ECU connector terminal No. 1/2 and the C-223 knee air bag module connector terminal No. 1/2.

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 ).