What Does My Car’s Oxygen Sensor Do?

What does an oxygen sensor do?Your check-engine light comes on, and your car heaves forward, tries to stall, heaves forward again. This two-step process continues, but you’re able to make your way home. You have no clue what caused the problem.

A good place to start looking for the problem is your car’s oxygen sensor, also known as an O2sensor. If you have a fuel-injected engine, it’s likely that you have an O2 sensor (most vehicles from 1990 and later do). You can also find that information in your owner’s manual.

Oxygen Sensors and Fuel-Injected Engines

An oxygen sensor measures the proportion of oxygen to gas and ensures your engine isn’t running too lean (not enough gas in the mixture) or too rich (too much gas). The sensor is located in the engine’s exhaust flow; it works with other exhaust parts, such as catalytic converters, to control engine emissions. While the engine control unit (ECU) adjusts the amount of fuel injected into the combustion chambers, the O2 unit takes readings, as many as 100 per second, and reports to the ECU to make adjustments and help your engine burn fuel more efficiently.

Symptoms of a failing oxygen sensor include:

  • The sensor light, or “check engine” light on the dashboard, remains on
  • You have a decrease in your car’s fuel efficiency, so you’re getting fewer miles per gallon
  • Your car stalls or hesitates during acceleration or it stalls often
  • The engine misfires or runs rough when idling

What Happens When the Oxygen Sensor Goes Bad?

It’s important to check the oxygen sensor often and replace it when needed. If it goes bad, it can affect the ECU and make it harder to get the right fuel mix for the engine. A good time to check this is when you have the oil changed.   

The failure of an oxygen sensor is mostly likely caused by:

  • The age of the sensor (which is usually the same age as the car)
  • High mileage of the car
  • Ongoing wear and tear of the car
  • Sensor damage from a contaminant, such as antifreeze, or a rich fuel mixture
  • Electrical problem (sensor isn’t grounded properly; wires have broken)

Sensor Lifespan

There are several types of O2 sensors in an engine’s exhaust system, the most common being the unheated sensor and the heated sensor. The lifetime of any O2 sensor depends on how the car is driven (jack-rabbit starts or slam-the-brakes stopping) and whether your car is properly maintained. In general, an unheated sensor lasts for 30,000 to 50,000 miles; a heated sensor is good for 70,000 to 100,000 miles.