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DTC B1B12: Driver’s Knee Air Bag (Squib) System (Squib Circuit Open)






caution If DTC B1B12 is set in the SRS-ECU, always diagnose the CAN main bus line.

CIRCUIT 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 knee air bag module will deploy.

DTC SET CONDITIONS


This DTC is set if there is abnormal resistance between the input terminals of the knee air bag module (squib).

TROUBLESHOOTING HITS



DIAGNOSIS
Required Special Tools:
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)

    • MB991824: Vehicle Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN Communication System)
  • MB991865: Dummy resistor
  • MB991884: Resister harness

STEP 1. Using scan tool MB991958, diagnose the CAN bus line.

(1)
caution To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
Connect scan tool MB991958. Refer to "How to connect the scan tool ."
(2)Turn the ignition switch to the "ON" position.
(3)Diagnose the CAN bus line.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the CAN bus line found to be normal?

Go to Step 2.

Repair the CAN bus line (Refer to GROUP 54C, Diagnosis ).

STEP 2. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1)Erase the DTC.
(2)Turn the ignition switch to the "ON" position.
(3)Check if the DTC is set.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the DTC 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 knee air bag module.
(1)Disconnect the negative battery terminal.

(2)Disconnect knee air bag module connector C-33. Use a flat-tipped screwdriver to unlock the locking button at the harness side connector by withdrawing it toward you in two stages, and then disconnect the connector.

(3)Connect special tool MB991865 to special tool MB991884.
(4)Connect special tool MB991884 to the C-33 harness side connector.
(5)Connect the negative battery terminal.
(6)Erase diagnostic trouble code memory, and then check the diagnostic trouble code.

Q. Is DTC B1B12 set?

Go to Step 4.

Replace the driver’s knee air bag module (Refer to ). Then go to Step 5.

STEP 4. Check the harness for open circuit between SRS-ECU connector C-122 and the knee air bag module C-33.
(1)Disconnect the negative battery terminal.

(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-122 SRS-ECU connector.

(3)Disconnect SRS-ECU connector C-122 and knee air bag module connector C-33, and measure at the wiring harness side. For connector C-33, use a flat-tipped screwdriver to unlock the locking button at the harness side connector by withdrawing it toward you in two stages, and then disconnect the connector.

(4)
caution Insert an insulator such as a cable tie to a depth of 4mm (0.16 inch) or more, otherwise the short spring will not be released.
Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch) thick] between terminals 1, 2 and the short spring to release the short spring.

(5)Connect C-33 harness side connector to special tool MB991884.

(6)Check for continuity between the following terminals. It should be less than 2 ohms.

  • SRS-ECU connector C-122 (terminal No.1) and the special tool (terminal No.1)
  • SRS-ECU connector C-122 (terminal No.2) and the special tool (terminal No.2)

Q. Does continuity exist?

Erase the diagnostic trouble code memory, and recheck if any DTC set. If DTC B1B12 set, replace the SRS-ECU (Refer to ). Then go to Step 5.

Repair the harness wires between SRS-ECU connector C-122 and knee air bag module connector C-33. Then go to Step 5.

STEP 5. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1)Erase the DTC.
(2)Turn the ignition switch to the "ON" position.
(3)Check if the DTC is set.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is DTC B1B12 set?
Return to Step 1.
The procedure is complete.