Code No.B1B12 Driver’s knee air bag module (squib) system (open circuit of squib circuit)
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If the diagnosis code B1B12 is set to SRS-ECU, be sure to diagnose the CAN bus line.
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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 knee air bag module (squib).
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The code is set when the open circuit occurs to the SRS-ECU driver’s knee air bag module (squib) circuit.
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- Poor contact of connector
- Open circuit to driver’s knee air bag module (squib) circuit
- Malfunction of SRS-ECU
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STEP 1. M.U.T.-III CAN bus diagnostics.
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Use M.U.T.-III to diagnose the CAN bus lines.
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Q.
Is the check result normal?
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 Go to Step 2.
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 Repair the CAN bus line (Refer to GROUP 54C - Troubleshooting  ).
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STEP 2. Check whether the diagnosis code is reset.
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(1)Connect the negative battery terminal.
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(2)After erasing the diagnosis code memory, check the diagnosis code again.
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(3)Disconnect the negative battery terminal.
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Q.
Is the diagnosis code No. B1B12 set?
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Go to Step 3.
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Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
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STEP 3. Diagnosis check by dummy resistor connection.
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(1)Check that the negative battery terminal is disconnected. If the negative battery terminal is connected, disconnect it.
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(2)Use the flat-tipped screwdriver to pull out the locking button of harness side connector. After releasing the lock, disconnect the C-25 harness side connector.
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(3)Connect the special tool dummy resistor (MB991865) to the special tool resistor harness (MB991884).
(4)Connect the special tool resistor harness to the C-25 harness side connector.
(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. B1B12 set?
Go to Step 4.
Replace the driver’s knee air bag module (Refer to ).
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STEP 4. Resistance measurement at the C-122 SRS-ECU connector and the C-25 knee air bag module connector.
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(1)Check that the negative battery terminal is disconnected. If the negative battery terminal is connected, disconnect it.
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(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.
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(3)flat-tipped screwdriver to pull out the locking button of harness side connector. After releasing the lock, disconnect the C-25 harness side connector.
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(4)Connect special tool resistor (MB991884) to the removed C-25 harness side connector.
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(5)
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The short spring may not be released due to the insufficient insertion. Therefore, insert the insulator for 4 mm or more.
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Insert an insulator (width: 3 mm, thickness: 0.5 mm) such as cable tie between the terminal No. 1 and 2, and then release the short spring.
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(6)Take the measurements below at the resistor harness and C-122 harness side connector.
- Continuity between C-122 SRS-ECU connector terminal No. 1 and resistor harness connector terminal No. 1
- Continuity between C-122 SRS-ECU connector terminal No. 2 and resistor harness connector terminal No. 2
OK: Continuity (less than 2 Ω)
Q.
Is the check result normal?
Go to Step 5.
Repair the wiring harness between the C-122 SRS-ECU connector terminal No. 1/2 and the C-25 knee air bag module connector terminal No. 2/1.
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STEP 5. Check whether the diagnosis code is reset.
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Q.
Is the diagnosis code No. B1B12 set?
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Replace SRS-ECU (Refer to ).
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Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
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