OBD-II code · Powertrain (generic)
P0166 O2 Sensor Circuit No Activity / Slow Response (Bank 2 Sensor 3)
The ECU detects no switching or too slow a response from the third O2 sensor on bank 2. Typically aged or poisoned sensor or weak heater.
Is it safe to drive with P0166?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySensor aged or poisoned
- PossibleHeater circuit weak
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
Repair at a glance
- Difficulty
- Easy
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.3–1.5 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Oxygen Sensor B2s3, Oxygen Sensor Heater Circuit
Related codes
- P0134O2 Sensor Circuit No Activity / Slow Response (Bank 1 Sensor 1)
- P0140O2 Sensor Circuit No Activity / Slow Response (Bank 1 Sensor 2)
- P0146O2 Sensor Circuit No Activity / Slow Response (Bank 1 Sensor 3)
- P0154O2 Sensor Circuit No Activity / Slow Response (Bank 2 Sensor 1)
- P0160O2 Sensor Circuit No Activity / Slow Response (Bank 2 Sensor 2)
- P0163O2 Sensor Circuit Malfunction (Bank 2 Sensor 3)
- P0164O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3)
- P0165O2 Sensor Circuit High Voltage (Bank 2 Sensor 3)
- P0167O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 3)
- P0168Fuel Temperature Too High
- P0169Incorrect Fuel Composition
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.