INSPECTION PROCEDURE 2: Power supply circuit system
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To SRS-ECU, the power is supplied from two independent circuits (fuse No. 15 and 21) via ignition switch (IG1) <vehicles without keyless operation system> or IG1 relay <Vehicles with keyless operation system>.
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If the power is not supplied to SRS-ECU, the communication between M.U.T.-III and SRS-ECU cannot be established.
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- Damaged wiring harness and connectors
- Battery failure
- Malfunction of the charging system
- Malfunction of SRS-ECU
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STEP 1. Fuse Nos. 15, 21 check.
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Q.
Is the fuse in good condition?
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 Go to Step 3.
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 Go to Step 2.
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STEP 2. Fuse open circuit check
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(2)Turn the ignition switch to the "ON" position, wait for at least one minute, and then turn the switch OFF.
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Q.
Is the fuse in good condition?
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Go to Step 3.
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Repair the wiring harness IG1A line between the junction block connector and SRS-ECU connector, IG1B line between the junction block connector terminal No. 8 and the SRS-ECU connector, and replace the fuse.
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STEP 3. Resistance measurement at the SRS-ECU connector.
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(1)Disconnect the SRS-ECU connectors.
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(2)Take the measurements below at the wiring harness side connectors.
- Continuity GND2 line between wiring harness side connector and body earth
OK: Continuity (less than 2 Ω)
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Q.
Is the check result normal?
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Go to Step 4.
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Repair the wiring harness GND2 line between the SRS-ECU connector and the body earth.
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STEP 4. Voltage measurement at the SRS-ECU connector (IG1A, IG1B line).
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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)Connect the negative battery terminal.
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(5)Take the measurements below at the harness side connector.
- Voltage IG1A, IG1B line between the SRS-ECU connector and the body earth
OK: 9 V or more
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(6)Disconnect the negative battery terminal.
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Q.
Is the check result normal?
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Go to Step 6.
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Go to Step 5.
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STEP 5. Resistance measurement at the SRS-ECU connector (IG1A, IG1B line).
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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)
- Continuity IG1A line between junction block connector and SRS-ECU connector
- Continuity IG1B line between junction block connector and SRS-ECU connector
OK: Continuity (less than 2 Ω)
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Q.
Is the check result normal?
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Go to Step 6.
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Repair the wiring harness IG1A line between the junction block connector and the SRS-ECU connector, IG1B line between the junction block connector and SRS-ECU connector.
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STEP 6. Trouble symptom check.
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Q.
Is the communication between M.U.T.-III and SRS-ECU possible?
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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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Replace SRS-ECU (Refer to ).
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