Code No.B1B21 Right curtain air bag module (squib) system (shorted to squib circuit power supply)












caution If the diagnosis code B1B21 is set to SRS-ECU, be sure to diagnose the CAN bus line.

OPERATION
In case of side collision, when the impact exceeding the threshold is applied to the vehicle, and when the impact is simultaneously detected (turned ON) by the side impact sensor as well as by the analogue G-sensor in SRS-ECU, the electric current is supplied from SRS-ECU to the curtain air bag module (squib) of impacted side.

TROUBLE JUDGEMENT
The code is set when the SRS-ECU curtain air bag module (squib) is shorted to power supply.

PROBABLE CAUSES

  • Damaged wiring harness and connector
  • Curtain air bag module (squib) harness shorted to power supply
  • Malfunction of SRS-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostic.
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. B1B21 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)Disconnect the D-11 intermediate connector unlock the connector by sliding the locking button to the direction of the arrow as shown in the figure, and then 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 probe of resistor harness, to which the dummy resister is installed, from the back of D-11 intermediate connector (floor wiring harness side).
(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. B1B21 set?

Go to Step 4.

Go to Step 5.

STEP 4. Voltage measurement at the C-121 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-121 SRS-ECU connector.

(3)
danger To release the SRS-ECU connector short spring in the following operations, disconnect this D-11 intermediate connector, and keep the squib circuit shorted.
Disconnect the D-11 intermediate connector unlock the connector by sliding the locking button to the direction of the arrow as shown in the figure, and then disconnect the 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 an insulator (width: 3 mm, thickness: 0.5 mm) such as cable tie between the terminal 39/40 and the short spring, and release the short spring.
(5)Connect the negative battery terminal.
(6)Ignition switch: ON
(7)Measure the voltage between the C-121 wiring harness side connector terminal No. 39/40 and the body earth.
OK: 0 V
(8)Disconnect the negative battery terminal.

Q. Is the check result normal?

Go to Step 6.

Repair the wiring harness.

STEP 5. Voltage measurement at the D-11 intermediate connector.
(1)Check that the negative battery terminal is disconnected. If the negative battery terminal is connected, disconnect it.

(2)
danger To release the D-11 intermediate connector short spring in the following operations, disconnect the F-06 harness side connector beforehand, and keep the squib circuit shorted.
Use the flat-tipped screwdriver to pull out the locking button of harness side connector. After releasing the lock, disconnect the F-06 harness side connector.

(3)Disconnect the D-11 intermediate connector unlock the connector by sliding the locking button to the direction of the arrow as shown in the figure, and then disconnect the connector.

(4)Because the short spring is installed to the D-11 intermediate connector (curtain air bag harness side), insert an insulator (width: 3 mm, thickness: 0.5 mm) such as cable tie to the location shown in the figure, and release the short spring.
(5)Connect the negative battery terminal.
(6)Ignition switch: ON
(7)
caution Do not insert a probe directly into the terminal from the connector front side as the connector contact pressure may be weakened.
Check the continuity between the D-11 intermediate connector (curtain air bag harness side) terminal No. 1/2 and the body earth.
OK: 0 V
(8)Disconnect the negative battery terminal.

Q. Is the check result normal?

Replace the curtain air bag module (squib) (Refer to ).

Repair the wiring harness.

STEP 6. Check whether the diagnosis code is reset.

Q. Is the diagnosis code No. B1B21 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 ).