Code result
P0166
O2 Sensor Circuit No Activity Detected
Moderate severity
What it means
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?
Use caution
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical.
Most likely causes
Sensor aged or poisoned
highOne of the most commonly reported causes for this code — check this first.
Heater circuit weak
mediumA plausible cause — test and verify before replacing parts.
Related help
Get the full diagnosis
Add your vehicle and see step-by-step repair help, recalls, and TSBs in Wrenchify.
Diagnose P0166 freeNo credit card required