by Kenda Robertson

Created on: December 28, 2010   Last Updated: December 29, 2010

If your vehicle is running a little rough and the check engine light on the car’s dashboard flashes off and on and then stays on, it could be a bad oxygen sensor. In some cases, the vehicle may idle fine with the check engine light on, but in fact, an oxygen sensor still could be the problem.

Most vehicles built within the last 25 years have at least one oxygen sensor and those built since 1996 have two or more. Some newer high-performance engines have an oxygen sensor for each cylinder, which could translate to as many as ten oxygen sensors. In this case, several may need to be replaced at one time as they tend to rely on each other.

The oxygen sensor is part of the exhaust system and is designed to monitor the amount of oxygen in the exhaust. This helps to keep the engine running efficiently. A bad sensor left unchanged can lead to lower gas mileage, pollution and other engine problems down the road.

Start with a Diagnostic Test

While there are several problems that could cause a check engine light to come on, the oxygen sensor is at the top of the list. But to know this for certain, it is necessary to get a diagnostic test of your engine. Owners can take their cars to a dealer or repair shop and pay anywhere from $50 to over $100 for a diagnostic test, depending on the shop and the car. However, some auto parts stores, such as AutoZone, want people to buy from their store, so they may offer a free diagnostic check test, which takes just a few minutes.

Once the problem has been determined to definitely be an oxygen sensor and the appropriate one to be changed is identified, the vehicle owner can either buy the part from a local parts store or order from an online discount company, such as RockAuto.com. Prices for oxygen sensors can range from $20 to over $100 each, but car owners will save on labor and part markups by replacing the sensor themselves.

Replacing the Sensor

To replace a worn out oxygen sensor, the owner may want to check the owner’s repair manual and see exactly where the part is located. Most engines have two sensors, one located before and one after the catalytic converter. If the car has several sensors, more than one may need to be replaced, depending on the diagnostic test results.

No special tools are required to remove an old oxygen sensor unless it is stuck on or out of reach and then it may be helpful to use pliers. Simply grab and pull out the old part and insert the new part. Some engines may be crowded making this process a little more difficult, but usually can be removed with some extra effort. It is helpful to use zinc oxide ointment on the inserted end of the new oxygen sensor to make it easier to remove the next time it needs to be replaced.

After the new oxygen sensor has been changed, it is time to start the vehicle. It may take a few starts for the check engine light to go off.  If it doesn’t go off after a few starts, the owner should return to the place where the diagnostic test was done and ask them to shut off the light manually or test for another problem.

Once the oxygen sensor is installed and functioning properly, depending on the make/model of the vehicle and the miles on it, the engine should be purring along for another 30,000 miles or so before the sensor needs to be replaced. However, if only one sensor was replaced, the others may not be far behind in needing to be changed.

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