Code No.B1631 Knee air bag module (squib) system (short circuit
between squib circuit terminals)
caution |
- If diagnosis code B1631 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 knee air bag module
(squib).
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The code is set when the short
circuit occurs to between the terminals of SRS-ECU knee air
bag module (squib) circuit.
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- Damaged short spring *
- Short circuit between terminals of knee 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 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. B1631 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: knee air bag module,
SRS-ECU.
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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)After disconnecting the SRS-ECU connector,
connect it again.
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![](../../../img/52/AC609126AF00ENG.png)
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(3)Use the flat-tipped screwdriver
to pull out the locking button of wiring harness side
connector, and release the lock, connect the connector
again. (4)Connect the negative battery
terminal. (5)After erasing the diagnosis code memory,
check the diagnosis code again. (6)Disconnect the
negative battery terminal.
Q.
Is diagnosis code No. B1631 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/AC609126AF00ENG.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.
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![](../../../img/52/AC301553DQ00ENG.png)
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(3)Connect the dummy resistor
(Special tool: MB991865) to the resistor harness (Special
tool: MB991884). (4)Connect the resistor harness (special
tool) to knee air bag module connector. (5)Connect the
negative battery terminal. (6)After erasing the diagnosis
code memory, check the diagnosis code again.
Q.
Is diagnosis code No. B1631 set?
Go to Step
5.
Replace
the knee air bag module (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)Disconnect the SRS-ECU connector.
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![](../../../img/52/AC609126AF00ENG.png)
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(3)
danger |
To release the connector short
spring in the following operations, disconnect
this harness side connector, and keep the squib
circuit shorted.
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Use the flat-tipped screwdriver to pull out the
locking button of wiring harness side connector, and release
the lock.
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![](../../../img/52/ACE02056AB00ENG.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 an insulator (width: 3 mm, thickness: 0.5 mm)
such as cable tie between the KDS+, KDS- line, and
then release the short spring. (5)Take the measurements
below at the harness side connector.
- Continuity between the KDS+, KDS-
line
OK: No continuity
Q.
Is the check result normal?
Go to Step
6.
Repair
the wiring harnesses KDS+, KDS- line between the knee
air bag module 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. B1631 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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