OBD-II FAULT CODE
P0166
O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 3)
Meaning, symptoms, likely causes, diagnostic checks and repair guidance for P0166.
- Check Engine light
- Poor drivability or reduced fuel economy depending on fault
- Fuel economy may drop
- Faulty O2 sensor
- Heater circuit fuse/wiring fault
- Exhaust leak
- Engine running too rich/lean
- Scan all modules and record freeze-frame data before clearing codes
- Check battery voltage and related fuses
- Inspect O2 sensor wiring near exhaust heat
- Check heater power/ground and sensor response before replacement
- Repair wiring/fuse/exhaust leak or replace confirmed faulty oxygen sensor
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Disclaimer: Information is provided for general guidance only and may not apply to all vehicles. Always consult a qualified technician.