Code No.B1402
Driver’s air bag module (squib) system (shorted to squib
circuit earth)
caution |
If the diagnosis code B1402
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 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 input
terminal of SRS-ECU driver’s air bag module (squib)
shorted to earth.
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- Damaged clock spring
- Damaged wiring harness and connectors
- Driver’s air bag module (squib) harness
shorted to earth
- 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. B1402 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.
Q.
Is the diagnosis code No. B1402 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
clock spring harness side connector
DQ1-, DQ1+ line. (5)Connect the negative battery
terminal. (6)After erasing the diagnosis code memory,
check the diagnosis code again.
Q.
Is the diagnosis code No. B1402 set?
Go to Step
5
Replace
the clock spring (Refer to ).
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STEP 5. Resistance measurement at the SRS-ECU
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 SRS-ECU
connector. (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)
caution |
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)Take the measurements below at the SRS-ECU
harness side connector. Continuity between DQ1-,
DQ1+ line and body earth OK: No
continuity
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
reset.
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Q.
Is the diagnosis code No. B1402 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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