Code No.B1604
Seat belt pre-tensioner (driver’s side) (squib) system (open circuit of squib circuit)
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If the diagnosis code B1604
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 seat belt pre-tensioner (squib).
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The code is set when the open circuit occurs to the SRS-ECU seat belt pre-tensioner (driver’s
side) (squib) circuit.
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- Open circuit to seat belt pre-tensioner (driver’s side) (squib)
circuit
- Damaged wiring harness and connector
- 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 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. B1604 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. 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 D-28 <LHD> and D-03 <RHD> harness side connector.
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(3)Connect special tool dummy resistor (MB991865) to special tool resistor harness (MB991884).
(4)Connect the special tool resistor harness to the D-28 <LHD> and D-03 <RHD>
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 the diagnosis code No. B1604 set?
Go to Step 4.
Replace the seat belt with pre-tensioner (driver’s side) (Refer to ).
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STEP 4. Resistance measurement at the C-124 SRS-ECU connector and
the D-28 <LHD> and D-03 <RHD> seat belt 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)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 C-124
SRS-ECU connector.
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(3)
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To release the SRS-ECU connector short spring in the
following operations, disconnect this seat belt 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 D-28 <LHD> and D-03 <RHD> 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 terminal
54/55 the short spring, and release the short spring.
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(5)Connect special tool resistor harness (MB991884) to the removed D-28 <LHD>
and
D-03 <RHD>
harness side connector.
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(6)Take the measurements below at the resistor harness and C-124 harness side connector.
- Continuity between C-124 SRS-ECU connector terminal No.
54 and resistor harness connector terminal No. 2
- Continuity between C-124 SRS-ECU connector terminal No. 55 and resistor harness connector
terminal No. 1
OK: Continuity (less than 2 Ω)
Q.
Is the check result normal?
Go to Step 5.
Repair the wiring harness between the C-124 SRS-ECU connector terminal No. 54/55
and the D-28 <LHD> and D-03 <RHD> seat belt pre-tensioner connector terminal No. 1/2.
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STEP 5. Check whether the diagnosis code is reset.
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Q.
Is the diagnosis code No. B1604 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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