10 Bad O2 Sensor Symptoms (What to Look Out For)

The oxygen sensor communicates air-fuel ratio measurements inside a car’s engine to its PCM/ECU to adjust accordingly. It also accounts for barometric pressure, altitude, and ambient/engine temperature (among other things) to determine whether the engine burns a lean or rich mixture.

When an O2 sensor goes bad, it can no longer trigger accurate fuel injection levels, regulate exhaust gas, or ensure efficient fuel combustion. Consequently, the vehicle may release harmful environmental pollutants or carbon-based compounds – in addition to having subpar engine performance.

Because of how vital an oxygen sensor’s role is in overall vehicle performance and emissions, spotting bad O2 sensor symptoms early on has become a necessary skill for drivers. A persistent Check Engine Light, intermittent stalling, or poor gas mileage are just a few of the signs to watch out for. So, what are the symptoms of a bad O2 sensor?

Here are 10 common bad oxygen sensor symptoms:

1. Continually failed emission tests
2. Flashing or illuminated CEL (Check Engine Light)
3. Misfiring, rough idling, or stalling
4. Bad fuel economy/gas mileage
5. Poor engine performance
6. Engine noises
7. Black exhaust fumes
8. Sulfuric/rotten-egg smell from the exhaust
9. Sudden catalytic converter failure
10. Engine overheating

Never put off inspecting and replacing your vehicle’s O2 sensors if you experience any of these problems. These devices are typically located along the exhaust system or between the exhaust manifold and the catalytic converter. Faulty O2 sensors take at most 30 minutes to repair (including an ECU reset) and are pretty accessible. Should you feel uneasy replacing them on your own, seek the help of a professional mechanic or a vehicle owner who is more experienced.

Bad O2 Sensor Symptoms