Code No.B1401: Driver’s Air Bag Module (1st Squib) System Fault 2 (Open in the Squib Circuit)

caution

If diagnosis code B1401 is set in the SRS-ECU, always diagnose the CAN main bus line.

OPERATION

The SRS-ECU judges how severe a collision is by detecting signals from the front impact sensors and the front air bag analogue 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 SRS air bag will inflate.
The ignition signal is input to the air bag module via the clock spring to inflate the air bag.

DIAGNOSIS CODE SET CONDITIONS

This diagnosis code is set if there is abnormal resistance between the input terminals of the driver’s side air bag module (squib). The most likely causes for this code to be set are the followings:

Open circuit in the driver’s air bag module (squib) or harness

Open circuit in the clock spring

Malfunction of connector contact

PROBABLE CAUSES

Open circuit in the clock spring
Open circuit due to improper neutral position of the clock spring
Open circuit in the driver’s air bag module (squib) circuit
Disengaged driver’s air bag module (squib) connector
Improper connector contact
Malfunction of the SRS-ECU

DIAGNOSIS

STEP 1. M.U.T.-III CAN bus diagnostics

Use the 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 54F, Diagnosis ).

STEP 2. Check whether the diagnosis code is reset.

Check again if the diagnosis code is set.

(1)Erase the diagnosis code.

(2)Ignition: LOCK (OFF) position to ON

(3)On completion, check that the diagnosis code is not reset.

Q. Is the diagnosis code 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 the driver’s air bag module (M.U.T.-III diagnosis code).

(1)Disconnect the negative battery terminal.

(2)Slide the outer housing of the driver’ s air bag module connector C-312 in the arrow direction shown, and disconnect the connector.

(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991866).
(4)

caution

Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.

Insert special tool MB991866 into clock spring side of driver’s air bag module connector C-312 (terminal No.1 and 2) by backprobing.
(5)Connect the negative battery terminal.
(6)Erase the diagnosis code memory, and check the diagnosis code.

Q. Is the checked diagnosis code set?

Go to Step 4 .

Replace the driver’s air bag module (Refer to

). Then go to Step 6 .

STEP 4. Check the clock spring (M.U.T.-III diagnosis code).

(1)Disconnect the negative battery terminal.

(2)Disconnect the clock spring connector C-309.

(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991866).
(4)

caution

Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.

Insert special tool MB991866 into harness side of clock spring connector C-309 (terminal No.4 and 3) by backprobing.
(5)Connect the negative battery terminal.
(6)Erase the diagnosis code memory, and check the diagnosis code.

Q. Is the checked diagnosis code set?

Go to Step 5 .

Replace the clock spring (Refer to

). Then go to Step 6 .

STEP 5. Check the harness between the SRS-ECU connector C-119 (terminal No.36 and 37) and the clock spring connector C-309 (terminal No.3 and 4) for open circuit.

(1)Disconnect SRS-ECU connector C-119 and clock spring connector C-309.

(2)

caution

Do not insert a test probe into the terminal from its front side directly, as the connector contact pressure may be weakened.

Check for continuity between the following terminals.

SRS-ECU connector C-119 (terminal No.36) and the clock spring connector C-309 (terminal No.3)
SRS-ECU connector C-119 (terminal No.37) and the clock spring connector C-309 (terminal No.4)

OK: Less than 2 Ω

Q. Are the check results normal?

Erase the diagnosis code memory, and check the diagnosis code. If diagnosis code B1401 set, replace the SRS-ECU (Refer to

). Then go to Step 6 .

Replace the harness wires between SRS-ECU connector C-119 and clock spring connector C-309. Then go to Step 6 .

STEP 6. Check whether the diagnosis code is reset.

Q. Is diagnosis code B1401 set?

	Return to Step 1 .

	The procedure is complete.