Code No.B1401: Driver’s air bag (1st squib) open-circuited
Code No.B1481: Driver’s air bag (2nd squib) open-circuited












caution If diagnosis code B1401 <1st squib> or B1481 <2nd squib> 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 analog 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 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 diagnosis code
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 54D, 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.
(1)Disconnect the negative battery terminal.

(2)Slide the outer housing of the driver’ s air bag module connector D-304 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 D-304 (terminal No.1 and 2 <1st squib> or terminal No.3 and 4 <2nd squib>) by backprobing.
(5)Connect the negative battery terminal.
(6)
caution Always diagnosis code B1481 is set when checking diagnosis code B1401. This is because the second side terminal is isolated when checking it, diagnosis code B1481 is set but this is not a fault. In addition, always diagnosis code B1401 is set when checking diagnosis code B1481 because the first side terminal is isolated.
Erase the diagnosis code from 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.
(1)Disconnect the negative battery terminal.
(2)Disconnect the clock spring connector D-306.

(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 D-306 (terminal No.4 and 3 <1st squib> or terminal No.1 and 2 <2nd squib>) by backprobing.
(5)Connect the negative battery terminal.
(6)
caution Always diagnosis code B1481 is set when checking diagnosis code B1401. This is because the second side terminal is isolated when checking it, diagnosis code B1481 is set but this is not a fault. In addition, always diagnosis code B1401 is set when checking diagnosis code B1481 because the first side terminal is isolated.
Erase the diagnosis code from 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. Resistance measurement between the SRS-ECU connector D-24 (terminal No.36 and 37 <1st squib> or terminal No. 33 and 34 <2nd squib>) and the clock spring connector D-306 (terminal No.3 and 4 <1st squib> or terminal No.1 and 2 <2nd squib>) for open circuit.
(1)Disconnect the negative battery terminal.
(2)Disconnect SRS-ECU connector D-24.
(3)
danger To release SRS-ECU connector short spring in the following operations, disconnect this clock spring connector, and keep the squib circuit shorted.
Disconnect clock spring connector D-306.


(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 36, 37 <1st squib> or 33, 34 <2nd squib> 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 the following terminals.
<1st squib>
  • SRS-ECU connector D-24 (terminal No.36) and the clock spring connector D-306 (terminal No.3)
  • SRS-ECU connector D-24 (terminal No.37) and the clock spring connector D-306 (terminal No.4)
<2nd squib>
  • SRS-ECU connector D-24 (terminal No.33) and the clock spring connector D-306 (terminal No.1)
  • SRS-ECU connector D-24 (terminal No.34) and the clock spring connector D-306 (terminal No.2)
OK: Continuity (Less than 2 Ω)

Q. Are the check results normal?

Erase the diagnosis code from memory, and check the diagnosis code. If diagnosis code B1401 <1st squib> or B1481 <2nd squib> set, replace the SRS-ECU (Refer to ). Then go to Step 6.

Replace the harness wires between SRS-ECU connector D-24 and clock spring connector D-306. Then go to Step 6.

STEP 6. Check whether the diagnosis code is reset.

Q. Is diagnosis code B1401 <1st squib> or B1481 <2nd squib> set?
Return to Step 1.
The procedure is complete.