Recently I was having issues with my 2002 Pontiac Grand AM GT. It was idling very odd and had a 500 RPM lope which made the car sound like it was struggling to stay running. My gas Mileage was about 12 MPG roughly 50% of the EPA estimated 25 mpg when it was new. Checking the codes I saw that an O2 (oxygen) sensor was throwing a code, so I decided to change it. Turns out there are 2 sensors that you can change the upstream and the downstream. The one that typically goes bad and causes fuel consumption to skyrocket is the upstream, luckily it is also the cheaper of the 2. $50.00 at Autozone.
So I purchased the sensor and promptly went home to youtube how to replace the sensor, to no avail. Not a single video or adequate description. So for anybody curious here is the walkthrough.
A couple of items to keep in mind, an O2 sensor requires a special socket to attach/detach, if you do not have one (you probably dont) AutoZone will let you rent parts for a deposit, this can be done easily in the parking lot so no worries. Looking at your engine the 02 sensor is going to be behind the engine, closest to the cabin of the vehicle. Open up your new sensor to get a feel for how it should look. The sensor can be found just below the rear set of spark plug wires. It is best to detach these so that you have a lot of room to work. *Mind the order in which they are plugged in, trust me if you do not put them back in the correct order you will know about it before you drive off*
Next unplug the sensor from the power connection, very easy, mine just slid right off. You may need a flathead screwdriver to accomplish this though. Autozone will have a special tool for removing the oxygen sensor, but unless you are exremely strong you probably wont be able to break the O2 sensor loose. They should have a breaker bar and a special socket that will allow you to use leverage to loosen the sensor. Once that is removed note the carbon that has built up on the sensor.
What is happening is the sensor is not telling the onboard computer the correct oxygen levels, which then causes the computer to inject more fuel to compensate. Thus driving down your MPG, fouling spark plugs, killing engine peformance. The steps for installing the new sensor are simple. First screw in the sensor with your fingers until it is fingertight. Then use the breaker bar (or tool if you are a world class bodybuilder) and tighten the sensor down. Connect the sensor to the power connector and replace the spark plugs in the exact order that they were in originally.
Starting the engine you should notice that the car starts much faster, idles a lot smoother and doesnt emit excessive exhaust/smelly exhaust. The true test is to see what your Mileage goes up to. Go fill up your vehicle to full, drive around for a couple of days. Trust me when I say that if your gas mileage was as bad as mine, if replacing the o2 sensor worked, you will know it really quick. Currently I am almost up to the EPA estimated MPG for a 2002 Pontiac grand up of 25 MPG, my average is 22. Fully 50% increase just by changing a $50 part.