CODE NO. B1B00 Driver’s air bag module (1st squib) system (shorted to squib circuit earth)
CODE NO. B1B04 Driver’s air bag module (2nd squib) system (shorted to squib circuit earth)












caution If the diagnosis code B1B00 (1st squib) or B1B04 (2nd 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 and passenger’s (front) air bag modules (squibs).

TROUBLE JUDGMENT
The code is set when the input terminal of SRS-ECU driver’s air bag module (squib) shorted to earth.

PROBABLE CAUSES

  • Damaged clock spring
  • Damaged wiring harness and connectors
  • Driver’s air bag module (squib) harness shorted to earth
  • Malfunction of SRS-ECU

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. B1B00 or B1B04 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. 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)Slide the outer housing of the C-205 driver’s air bag module connector 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 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 terminals Nos. 1 and 2 (1st squib) and Nos. 3 and 4 (2nd squib) of C-205 driver’s air bag module connector.
(5)Connect the negative battery terminal.
(6)
caution At the diagnosis code B1B00 check, always the diagnosis code B1B06 is set. The diagnosis code B1B06 is set because the 2nd side terminal is disconnected at the time of inspection, but it does not indicate any abnormality. Also, at the time of diagnosis code B1B04 check, always the diagnosis code B1B02 is set because the 1st side terminals are disconnected.
After erasing the diagnosis code memory, check the diagnosis code again.

Q. Is the diagnosis code No. B1B00 or B1B04 set?

Go to Step 4.

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

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)Disconnect the C-207 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-207 harness side connector terminals Nos. 3 and 4 (1st squib) and Nos. 1 and 2 (2nd squib).
(5)Connect the negative battery terminal.
(6)
caution At the diagnosis code B1B00 check, always the diagnosis code B1B06 is set. The diagnosis code B1B06 is set because the 2nd side terminal is disconnected at the time of inspection, but it does not indicate any abnormality. Also, at the time of diagnosis code B1B04 check, always the diagnosis code B1B02 is set because the 1st side terminals are disconnected.
After erasing the diagnosis code memory, check the diagnosis code again.

Q. Is the diagnosis code No. B1B00 or B1B04 set?

Go to Step 5.

Replace the clock spring (Refer to ).

STEP 5. Resistance measurement at the C-32 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-32 SRS-ECU connector.
(3)Disconnect the C-207 clock spring connector.
(4)Take the measurements below at the C-32 harness side connector.
Continuity between terminal No. 5/6 and body earth (1st squib)
Continuity between terminal No. 9/10 and body earth (2nd squib)
OK: No continuity

Q. Is the check result normal?

Go to Step 6.

Repair the wiring harnesses between the C-207 clock spring connector terminal No. 3/4 and the C-32 SRS-ECU connector terminal No. 6/5 (1st squib), and between the C-207 clock spring connector terminal No. 1/2 and the C-32 SRS-ECU connector terminal No. 9/10 (2nd squib).

STEP 6. Check whether the diagnosis code is reset.

Q. Is the diagnosis code No. B1B00 or B1B04 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 ).