How To Replace an Oxygen Sensor

The number one cause of the dreaded "Check Engine" light that pops up on your dash and strikes fear deep in your wallet is a failed oxygen (O2) sensor. The oxygen sensor monitors the O2 in the exhaust system and determines if the mix is too rich or too thin. When a sensor fails you will most likely first notice a dramatic drop in gas mileage (up to 40%) and of course eventually the "check engine" warning will be displayed.

• Code scanner
• Correct oxygen sensor replacement
• Floor jack, jack stands or ramps
• Ratchet wrench
• Special O2 sensor attachment for ratchet wrench
• Penetrating oil
• Owner's manual

The first thing you will want to do is determine that you actually have a failed oxygen sensor. To do this you will need to plug in a code scanner to your ECU. Cars may have several sensors and your scan should be able to single out the problem child.

Next you need the correct replacement and sometimes it's best to remove the old sensor so you have something to compare to. Sensors and their connections to their wiring harness have changed over the years. Older cars may have a single wire while newer ones may have four. Equally important is the connection or plug in to the wiring harness. Not all manufacturers use the same design so if you use an aftermarket sensor you will probably have to cut the plug from the old sensor and solder it on to the new.

Know going into this project that the hardest part will be removing the old sensor. These units live in a very rough environment exposed to dirt, grime, salt, water and extreme heat and they may appear to be welded to the exhaust. Some experts advise dousing the sensor with penetrating oil and letting it work for up to a day before attempting to remove it.

1. Elevate the car on secure devices designed for the purpose.
2. Locate the failed sensor and spray it down with penetrating oil. Slide out from under and give the oil at least an hour to work.
3. Put the O2 sensor attachment on your ratchet wrench and attempt to remove the old sensor. If it still won't budge give it another shot of oil and try again in 30 minutes.
4. When you are able to remove the sensor, follow the wires to the point where they meet the wiring harness and unplug the sensor.
5. Your new sensor should have antiseize compound on the threads. If it doesn't, add some to prevent a repeat of the struggle you just went through pulling the old sensor. There should be a "guard" covering the sensor itself. When you are ready to put the new sensor in the exhaust line remove the "guard" and insert the sensor making sure it doesn't touch anything in the process. Tighten the unit by hand then give it a quarter turn with the ratchet wrench.
6. Connect the new unit to the wiring harness by plugging it in.

Was it worth it? By doing it yourself you saved the mark up on the sensor and about $150.00 in labor. And you got the satisfaction that comes from doing the job yourself.

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