Code No. B1620: Driver’s
lap pre-tensioner (squib) system (open circuit of squib circuit)
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If the diagnosis code No.
B1620 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 lap pre-tensioner (squib).
TROUBLE JUDGEMENT
The code is set when the open circuit occurs to
the SRS-ECU driver’s lap pre-tensioner
(squib) circuit.
PROBABLE CAUSES
- Poor contact of connector
- Open circuit to lap pre-tensioner (squib) circuit
- 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 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. B1620 set?
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Go to Step 3.
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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
(MB991884).
(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. B1620 set?
Go to Step 4.
Replace the seat belt with
pre-tensioner.
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STEP 4. Resistance measurement at the SRS-ECU connector and the lap
pre-tensioner 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 PD2+,
PD2-, and then release the short spring.
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(5)Connect special tool resistor harness
(MB991884) to the removed lap pre-tensioner harness
side connector.
(6)Take the measurements below at the resistor harness
and SRS-ECU harness side connector.
- Continuity PD2+
line between SRS-ECU connector
and lap pre-tensioner harness connector
- Continuity PD2- line between SRS-ECU connector and lap pre-tensioner
harness connector
OK: Continuity (less than 2 Ω)
Q.
Is the check result normal?
Go to Step 5.
Repair the wiring harness PD2+,
PD2- line between the SRS-ECU connector
and the lap pre-tensioner connector.
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STEP 5. Check whether the diagnosis code is set again.
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Q.
Is diagnosis code No. B1620 set?
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Replace SRS-ECU.
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Intermittent malfunction.
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