Code No. B1401: Driver’s
air bag module (squib) system (open circuit of squib circuit)
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If diagnosis code No. B1401
is set in the 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 driver’s air bag module (squib).
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The code is set when the open circuit occurs to the SRS-ECU driver’s air bag
module (squib) circuit.
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- Open circuit in the clock spring
- Open circuit due to improper neutral position of the clock spring
- Open circuit to driver’s air bag module (squib) circuit
- Disengaged driver’s air bag module (squib) connector
- Poor contact of connector
- 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 set again.
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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 diagnosis code No. B1401 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 wiring harness side
connector, and release the lock.
(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness
(MB991866).
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(4)
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Do not insert a probe directly into the terminal from the connector
front side as the connector contact pressure may be weakened.
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Insert the resistor harness probe (special tool) as shown.
(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 diagnosis code No. B1401 set?
Go to Step 4.
Replace the driver’s air bag module (Refer to ).
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STEP 4. 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)Disconnect the clock spring connector.
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(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991866).
(4)
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Do not insert a probe directly into the terminal from the connector
front side as the connector contact pressure may be weakened.
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Insert the resistor harness probe from the back of harness side connector DQ1-, DQ1+ line.
(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 diagnosis code No. B1401 set?
Go to Step 5.
Replace the clock spring (Refer to ).
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STEP 5. Resistance measurement at the SRS-ECU and the C-313 clock
spring connectors
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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)Disconnect the SRS-ECU connector. <Except vehicles for Europe (double
cab) and except vehicles with ERA-GLONASS system>
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(3)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 SRS-ECU
connector. <Vehicles for Europe (double cab) and vehicles with ERA-GLONASS system>
(4)
| caution |
To release SRS-ECU connector short spring in the following
operations, disconnect this clock spring connector, and keep the squib circuit shorted.
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Disconnect the clock spring 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 the insulator (width: 3 mm, thickness: 0.5 mm) such as cable tie between the DQ1-,
DQ1+ line, and then release the short spring.
(6)
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Do not insert a probe directly into the terminal of clock spring connector
harness side connector from the connector front side as the connector contact pressure may be
weakened.
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Take the measurements below at the SRS-ECU connector and clock spring connector harness
side connectors.
- Continuity DQ1- line between SRS-ECU connector and clock
spring connector
- Continuity DQ1+ line between SRS-ECU connector and clock spring connector
OK: Continuity (less than 2 Ω)
Q.
Is the check result normal?
Go to Step 6.
Repair the wiring harnesses DQ1-, DQ1+ line between the clock spring
connector and the SRS-ECU connector.
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STEP 6. Check whether the diagnosis code is set again.
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Q.
Is diagnosis code No. B1401 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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