Code No. B1621
Driver’s lap pre-tensioner (squib) system (shorted to squib circuit
earth)
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If diagnosis code No. B1621
is stored in the SRS-ECU, be sure to diagnose the CAN bus line.
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OPERATION
Only when the frontal collision impact that exceeds 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 lap pre-tensioner (squib).
TROUBLE JUDGEMENT
The code is stored when the input terminal of
SRS-ECU lap pre-tensioner (squib) is shorted
to earth.
PROBABLE CAUSES
- Damaged wiring harness and connector
- Lap pre-tensioner (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 stored 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. B1621 stored?
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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 harness side connector.
After releasing the lock, disconnect the lap pre-tensioner harness side
connector.
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(3)Connect the special tool dummy resistor
(MB991865) to the special tool resistor harness (MB991866).
(4)Connect
the special tool resistor harness to the lap pre-tensioner harness side
connector.
(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. B1621 stored?
Go to Step 4.
Replace the seat belt with
pre-tensioner (Refer to ).
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STEP 4. 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)
| danger |
To release the SRS-ECU connector short spring in
the
following operations, disconnect this lap pre-tensioner connector, and
keep the squib circuit
shorted.
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Use the flat-tipped screwdriver to pull out the locking button of
harness side connector.
After releasing the lock, disconnect the lap pre-tensioner harness side
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 an insulator (width: 3 mm, thickness: 0.5 mm) such as cable
tie between the PA2+,
PA2- line and the short spring and release the short spring.
(5)Take the
measurements below at the SRS-ECU harness side
connector.
- Continuity between PA2+, PA2- line and body
earth
OK: No continuity
Q.
Is the check result normal?
Go to Step 5.
Repair the wiring harness PA2+,
PA2- line between the SRS-ECU connector
and the lap pre-tensioner connector.
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STEP 5. Check whether the diagnosis code is stored again.
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Q.
Is diagnosis code No. B1621 stored?
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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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