Code No.B1401 Driver’s air bag module (squib) system (open
circuit of squib circuit)
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If diagnosis code 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)
| caution |
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)
| caution |
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.
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(3)
| 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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(4)
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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.
(5)
| caution |
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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