Code No.B1400
Driver’s air bag module (squib) system (short circuit between
squib circuit terminals)
caution |
- If
the diagnosis code No. B1400 (squib) is set to
SRS-ECU, be sure to diagnose the CAN bus
line.
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OPERATION
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).
TROUBLE JUDGEMENT
The code is set when the short circuit
occurs to between the terminals of SRS-ECU driver’s
air bag module (squib) circuit.
PROBABLE CAUSES
- Damaged short spring *
- Short circuit in the clock spring
- Short circuit between terminals of driver’s air bag module
(squib) circuit
- Damaged connector(s)
- Malfunction of SRS-ECU
note |
*: The squib circuit connectors
integrate a short spring (which prevents the
air bags from being unintentionally deployed because of
static electricity by shorting the positive
wire to the earth wire in the squib circuit when the
connectors are disconnected). Therefore,
when the above codes are set, the short spring may not be
released due to the damaged connector
even when the connectors are connected.
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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. B1400 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. Connector check: SRS-ECU, clock spring,
driver’s air
bag module.
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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. After disconnecting the
SRS-ECU connector, connect it again. (3)After
disconnecting clock spring, connect it again.
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(4)Disconnect the driver’s
air bag module connector using the slotted (-) screwdriver
to pull out the locking button to the direction of the
arrow, and connect it again. (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. B1400 set?
Go to Step
4.
Replace
the connector concerned.
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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)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 the diagnosis code No. B1400 set?
Go to Step
5.
Replace
the driver’s air bag module (Refer to )
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STEP 5. 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 the diagnosis code No. B1400 set?
Go to Step
6.
Replace
the clock spring (Refer to ).
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STEP 6. 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 harness
side connector. Continuity between DQ1-, DQ1+ line
OK: No continuity
Q.
Is the check result normal?
Go to Step
7.
Repair
the wiring harnesses between DQ1-, DQ1+ line the clock
spring
connector and the SRS-ECU connector.
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STEP 7. Check whether the diagnosis code is
reset.
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Q.
Is the diagnosis code No. B1400 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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