P0166: No activity is detected in the oxygen-sensor circuit for bank 2, sensor 3.
Meaning, symptoms, causes and checks
No activity is detected in the oxygen-sensor circuit for bank 2, sensor 3. This is an activity-monitoring fault, distinct from a heater-circuit code.
Affected system: Powertrain
Symptoms
- Check Engine light
- Failed emissions inspection
- Possible rough running or increased fuel use
- Often little noticeable drivability change
Possible causes
- Faulty oxygen sensor or heater
- Exhaust leak or damaged sensor wiring
- Incorrect mixture affecting sensor response
- Connector, fuse, relay, or control-circuit fault
What to check
- Record codes, freeze-frame data, and monitor status
- Inspect the exhaust and complete sensor circuit
- Verify heater power, ground, and resistance to specification
- Compare sensor activity and fuel trims
- Complete the proper drive cycle after repair
- Inspect exhaust leaks, wiring, connectors, and heater power
- Graph oxygen-sensor response and compare banks
- Test the heater circuit and sensor signal
Also written as: P0166-00, P016600, PO166 (some scan tools add the fault-type byte, e.g. -00).