Code No.B1400: Driver’s Air Bag Module (1st Squib) System Fault 1 (Short Circuit between Terminals of the Squib Circuit)

caution

If diagnosis code B1400 <1st squib> or B1480 <2nd squib> is set in the SRS-ECU, always diagnose the CAN bus lines.

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:

Short circuit in driver’s air bag module (squib) or harness
Short circuit in the clock spring

PROBABLE CAUSES

Improper engaged connector or defective short spring*
Short circuit in the clock spring
Short circuit between the driver’s air bag module (squib) circuit terminals
Damaged connector(s)
Malfunction of the SRS-ECU

note

*: The squib circuit connectors integrate a "short" spring (which prevents the air bag from deploying unintentionally due to static electricity by shorting the positive wire to the earth wire in the squib circuit when the connectors are disconnected). (Refer to

). Therefore, if connector C-119, C-309 or C-312 is damaged or improperly engaged, the short spring may not be released when the connector is connected.

DIAGNOSIS PROCEDURE

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. M.U.T.-III diagnosis code

caution

To prevent damage to M.U.T.-III, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting M.U.T.-III.

(1)Turn the ignition switch to the "ON" position.

(2)Check if the diagnosis code is set.

(3)Turn the ignition switch to the "LOOK" (OFF) position.

Q. Is diagnosis code B1519 set?

	Go to Step 4 .

	Go to Step 5 .

STEP 4. Connector check: SRS-ECU connector C-119.

Q. Is the connector correctly engaged?

Go to Step 5 .

Engage the connector correctly. Then go to Step 10.

STEP 5. Connector check: SRS-ECU connector C-119, clock spring connector C-309 and driver’s air bag module connector C-312 (M.U.T.-III diagnosis code.)

(1)Disconnect the negative battery terminal.

(2)Disconnect connectors C-119, C-309 and C-312, and then reconnect them.
(3)Connect the negative battery terminal.
(4)Erase the diagnosis trouble code memory, and check the diagnosis trouble code.

Q. Is diagnosis code B1400 set?

Go to Step 6 .

The procedure is complete. It is assumed that diagnosis code B1400 set because connector C-119, C-309 or C-312 was engaged improperly.

STEP 6. 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 clock spring side of 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 7 .

Replace the driver’s air bag module (Refer to

). Then go to Step 10 .

STEP 7. 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 clock spring harness side connector C-309 (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 the checked diagnosis code set?

Go to Step 8 .

Replace the clock spring (Refer to

). Then go to Step 10 .

STEP 8. Check the driver’s air bag module circuit. Resistance measurement at SRS-ECU connector C-119.

(1)Disconnect SRS-ECU connector C-119.

(2)

danger

To prevent the air bag from deploying unintentionally, disconnect clock spring connector C-309 to short the squib circuit.

Disconnect clock spring connector C-309.

(3)

caution

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

Insert a cable tie [3 mm wide, 0.5 mm thick] between terminals 36, 37 and the short spring to release the short spring.

(4)

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-119 harness side connector terminals 36 and 37.
OK: Open circuit

Q. Is the check result normal?

Erase the diagnosis code memory, and check the diagnosis code. If diagnosis code B1400 set, replace the SRS-ECU (Refer to

). Then go to Step 10 .

Go to Step 9 .

STEP 9. Check the harness for short circuit between SRS-ECU connector C-119 (terminal No.36 and 37) and clock spring connector C-309 (terminal No.3 and 4).

Q. Are harness wires between SRS-ECU connector C-119 (terminal No.36 and 37) and clock spring connector C-309 (terminal No.3 and 4) in good condition?

Go to Step 10 .

Replace the harness wires between SRS-ECU connector C-119 and clock spring connector C-309. Then go to Step 10 .

STEP 10. Check whether the diagnosis code is reset.

Q. Is diagnosis code B1400 set?

	Return to Step 1 .

	The procedure is complete.