Code No.B1402: Driver’s air bag module (squib) system (short-circuited to the earth)

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 the driver’s air bag squib wire(s) are short-circuited to the earth.

PROBABLE CAUSES

Malfunction of the clock spring
Damaged harness wires and connectors
Short to the earth in the driver’s air bag module (squib) harness
Malfunction of the SRS-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check the diagnosis code by connecting a dummy resistor. (M.U.T.-III diagnosis code)

(1)Disconnect the negative battery terminal.

(2)By sliding the A section (in the figure) of air bag module connector C-303 in arrow direction, 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 air bag module connector C-303 by backprobing.
(5)Connect the negative battery terminal.
(6)Erase the diagnosis code memory, and check the diagnosis code.

Q. Is diagnosis code B1402 set?

Go to Step 2.

Replace the driver’s air bag module (Refer to

STEP 2. Check the diagnosis code by connecting a dummy resistor. (M.U.T.-III diagnosis code)

(1)Disconnect the negative battery terminal.

(2)Disconnect the clock spring connector C-305.

(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 harness side connector C-305 (terminal No.3 and 4) by backprobing.
(5)Connect the negative battery terminal.
(6)Erase the diagnosis code memory, and check the diagnosis code.

Q. Is diagnosis code B1402 set?

Go to Step 3.

Replace the clock spring (Refer to

STEP 3. Resistance measurement at the SRS-ECU connector C-131.

(1)Disconnect the negative battery terminal.

(2)Disconnect SRS-ECU connector C-131.

(3)

danger

To prevents the air bag from deploying unintentionally, disconnect the clock spring connector C-305 to short the squib circuit.

Disconnect the clock spring connector C-305.

(4)

caution

Insert an insulator such as a cable tie to a depth of 4 mm or more, otherwise the short spring will not be released.

Insert a cable tie [3 mm wide, 0.5 mm thick] between terminals 11, 12 and the short spring to release the short spring.

(5)

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 C-131 harness side connector terminals 11, 12 and body earth.
OK: Open circuit

Q. Is the check result normal?

Go to Step 4.

Repair the harness wires between SRS-ECU connector C-131 (terminal No.11 and 12) and clock spring connector C-305 (terminal No.3 and 4).

STEP 4. Check whether the diagnosis code is reset.

Q. Is diagnosis code B1402 set?

	Replace the SRS-ECU (Refer to ).

	An intermittent malfunction is suspected (Refer to GROUP 00, How to Cope with Intermittent Malfunction ).