Code No. B1400: Driver’s
air bag module (squib) system (short circuit between squib circuit
terminals)
caution |
- If
the diagnosis code No. B1400 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
driver’s air bag module (squib).
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The code is set when the short
circuit occurs to between the terminals of SRS-ECU
driver’s
air bag module (squib) circuit.
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- 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
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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.
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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)Disconnecting the SRS-ECU connector, connect it
again.
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(3)After disconnecting clock spring, connect it
again.
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![](../../../img/52/ACB04316AB00ENG.png)
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(4)Disconnect the driver’s
air bag module connector using the flat-tipped 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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![](../../../img/52/ACB04316AB00ENG.png)
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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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![](../../../img/52/AC905251AC00ENG.png)
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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.
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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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![](../../../img/52/AC905254AC00ENG.png)
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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.
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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)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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![](../../../img/52/ACF04632AD00ENG.png)
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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 DQ1-, DQ1+ line between 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.
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Intermittent
malfunction.
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