Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
2009 Lexus IS FFACTORY OEM SERVICE PROCEDURE
Diagnostic Trouble Code Chart
WARNING: This page is about a different car, the 2011 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
- DTCS FOR OCCUPANT CLASSIFICATION SYSTEM
If a trouble code is displayed during the DTC check, check the circuit listed for the code in the table below (Refer to the "See" listed for that circuit).
OCCUPANT CLASSIFICATION SYSTEMDTC Code Detection Item Trouble Area See B1771 Passenger Side Buckle Switch Circuit Malfunction 1. Front seat inner belt assembly RH (Passenger side buckle switch)
2. Floor wire No. 2
3. Front seat wire RH (for Power seat)
4. Occupant classification ECURefer to DTC B1771: Passenger Side Buckle Switch Circuit Malfunction B1780 Front Occupant Classification Sensor LH Circuit Malfunction 1. Front seat assembly RH (Front occupant classification sensor LH)
2. Front seat wire RH
3. Occupant classification ECURefer to DTC B1780: Front Occupant Classification Sensor LH Circuit Malfunction B1781 Front Occupant Classification Sensor RH Circuit Malfunction 1. Front seat assembly RH (Front occupant classification sensor RH)
2. Front seat wire RH
3. Occupant classification ECURefer to DTC B1781: Front Occupant Classification Sensor RH Circuit Malfunction B1782 Rear Occupant Classification Sensor LH Circuit Malfunction 1. Front seat assembly RH (Rear occupant classification sensor LH)
2. Front seat wire RH
3. Occupant classification ECURefer to DTC B1782: Rear Occupant Classification Sensor LH Circuit Malfunction B1783 Rear Occupant Classification Sensor RH Circuit Malfunction 1. Front seat assembly RH (Rear occupant classification sensor RH)
2. Front seat wire RH
3. Occupant classification ECURefer to DTC B1783: Rear Occupant Classification Sensor RH Circuit Malfunction B1785 Front Occupant Classification Sensor LH Collision Detection 1. Occupant classification ECU
2. Front seat assembly RH (Front occupant classification sensor LH)Refer to DTC B1785: Front Occupant Classification Sensor LH Collision Detection B1786 Front Occupant Classification Sensor RH Collision Detection 1. Occupant classification ECU
2. Front seat assembly RH (Front occupant classification sensor RH)Refer to DTC B1786: Front Occupant Classification Sensor RH Collision Detection B1787 Rear Occupant Classification Sensor LH Collision Detection 1. Occupant classification ECU
2. Front seat assembly RH (Rear occupant classification sensor LH)Refer to DTC B1787: Rear Occupant Classification Sensor LH Collision Detection B1788 Rear Occupant Classification Sensor RH Collision Detection 1. Occupant classification ECU
2. Front seat assembly RH (Rear occupant classification sensor RH)Refer to DTC B1788: Rear Occupant Classification Sensor RH Collision Detection B1790 Center Airbag Sensor Assembly Communication Circuit Malfunction 1. Occupant classification ECU
2. Center airbag sensor assembly
3. Floor wire No. 2
4. Front seat wire RHRefer to DTC B1790: Center Airbag Sensor Assembly Communication Circuit Malfunction B1793 Occupant Classification Sensor Power Supply Circuit Malfunction 1. Front seat assembly RH (Occupant classification sensors)
2. Front seat wire RH
3. Occupant classification ECURefer to DTC B1793: Occupant Classification Sensor Power Supply Circuit Malfunction B1794 Open in Occupant Classification ECU Battery Positive Line 1. Battery
2. ECU-B fuse
3. Floor wire No. 2
4. Front seat wire RH
5. Occupant classification ECURefer to DTC B1794: Open in Occupant Classification ECU Battery Positive Line B1795 Occupant Classification ECU Malfunction 1. Front seat inner belt assembly RH
2. Occupant classification ECURefer to DTC B1795: Occupant Classification ECU Malfunction B1796 Sleep Operation Failure of Occupant Classification ECU Occupant classification ECU Refer to DTC B1796: Sleep Operation Failure of Occupant Classification ECU
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.