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Will a Bad O2 Sensor Cause a Misfire?

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If you don’t remember from your high school chemistry class, O2 is the chemical symbol for oxygen. As the engine in your car is running, it puts out certain gases as part of the reaction of the combustible engine.

Oxygen is one of those gases, and to keep the engine running at optimal performance, your car needs to measure the amount of oxygen in the exhaust. But the big question in all this is, will a bad O2 sensor cause a misfire in your car?

What Does an O2 Sensor Do?

An O2 sensor does more than simply measure oxygen in your car’s exhaust. It also sends that information to the Powertrain Control Module, or PCM. The amount of O2 your car is exhausting will cause your car to adjust the air to fuel ratio to maximize its efficiency.

Other parts of the car that get adjusted are the fuel injectors and the engine timing. When the O2 sensor fails, there are several symptoms, including your check engine light, worse gas mileage than normal, and rough engine idling.

But will a bad O2 sensor cause a misfire?

Will a Bad O2 Sensor Cause a Misfire?

The short answer is yes, a bad O2 sensor can cause your engine to misfire. But why is that? As explained, the O2 sensor sends information to the PCM to adjust engine components to run the most efficiently.

One of the ways that an O2 sensor could be faulty is sending the wrong signals to the PCM which ends up causing a lean air/fuel mixture. A lean mixture means the engine is letting in too much air, but not enough fuel for the reaction in the chamber.

This causes the engine to misfire, particularly while it’s in idle.


While you could technically still drive a car with a bad O2 sensor, it’s not recommended. Not only will you be getting poor gas mileage and an engine that’s running rough, but you’re also damaging the environment by driving a car with a bad O2 sensor.

An engine could also stall with a bad O2 sensor and you certainly don’t want to be having issues of stalling while you’re out on the road.

It’s important to get the O2 sensor replaced right away, whether you are able to do it on your own, or have your trusted mechanic make the repairs. You can check our article on the cost of replacing an O2 sensor here.

If you suspect that you may have a bad O2 sensor, you should get it diagnosed and repaired immediately to prevent damage to your engine and the environment.