Code No.B1400 Driver’s air bag module (squib) system (short circuit between squib circuit terminals)


caution
  • If the diagnosis code No. B1400 (squib) 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 driver’s air bag module (squib).

TROUBLE JUDGEMENT
The code is set when the short circuit occurs to between the terminals of SRS-ECU driver’s air bag module (squib) circuit.

PROBABLE CAUSES

  • Damaged short spring *
  • Short circuit in the clock spring
  • Short circuit between terminals of driver’s air bag module (squib) circuit
  • Damaged connector(s)
  • Malfunction of SRS-ECU
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. B1400 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-313 clock spring, C-303 driver’s 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 C-313 clock spring, connect it again.

(4)Disconnect the C-303 driver’s air bag module connector using the slotted (-) screwdriver to pull out the locking button to the direction of the arrow, and connect it again.
(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. B1400 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 wiring harness side connector, and release the lock.
(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991866).

(4)
caution Do not insert a probe directly into the terminal from the connector front side as the connector contact pressure may be weakened.
Insert the resistor harness probe (special tool) as shown.
(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. B1400 set?

Go to Step 5.

Replace the driver’s air bag module (Refer to )

STEP 5. 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)Disconnect the C-313 clock spring connector.

(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991866).
(4)
caution Do not insert a probe directly into the terminal from the connector front side as the connector contact pressure may be weakened.
Insert the resistor harness probe from the back of C-313 harness side connector terminals Nos. 3 and 4.
(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. B1400 set?

Go to Step 6.

Replace the clock spring (Refer to ).

STEP 6. Resistance measurement 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)
caution To release SRS-ECU connector short spring in the following operations, disconnect this clock spring connector, and keep the squib circuit shorted.
Disconnect the C-313 clock spring 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 the insulator (width: 3 mm, thickness: 0.5 mm) such as cable tie between the terminals Nos. 5 and 6, and then release the short spring.
(5)Take the measurements below at the C-126 harness side connector.
Continuity between terminal No. 5 and No. 6
OK: No continuity

Q. Is the check result normal?

Go to Step 7.

Repair the wiring harnesses between the C-313 clock spring connector terminal No. 3/4 and the C-126 SRS-ECU connector terminal No. 5/6.

STEP 7. Check whether the diagnosis code is reset.

Q. Is the diagnosis code No. B1400 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 ).