My O2 sensor went out on my 98' at 53,000. They say it will cost $100 to fix, and if it is not replaced it will definately cause more damage. Does a bad sensor cause poor gas mileage or other performance problems? I haven't noticed a big performance change recently. Also how much should a sensor cost? Is it easy to replace yourself?

 

If the O2 sensor is bad, it can cause perf. problems, as EEC uses the amount of Oxy in exhaust gas to adjust injector duration. If sensor is bad, the EEC falls back onto its default table values, instead of fine tuning it. Replaced a sensor in a Dodge recently, was approx. 45$ for a Bosch. You will need the cut-away O2 sensor socket, maybe $8 or so, also available from parts store. Some break loose real easy, some are tougher. I have had some try to cross-thread on putting the new one in, due to carbon on the threads in the exhaust pipe, so thread in carefully and STRAIGHT, and all will be okay. Its an easy job, but you may want to go look where it is, first, to see if you can get to it. You will need to know WHICH one is bad, if you have a 97 or later, as there are multiple O2 sensors. Before catalytic converters, and after cats.

 

White,
I have had both O2 sensors replaced. I cost me about $75. a piece. What Granpa said happens with bad O2s is exactly what I was told.

 

Do you get an O2 sensor light when they go bad or is there another way to check?

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'97 F-150 4x4 4.6L Auto Off Road Moonlight Blue
Tow package, Westin Chrome Nerf bars, Color matched bug shield
Linex bed liner, Wizard Ultra White Headlights

 

If one of them gets far enough out of the working range, and stays there, the Check Engine light will come on. But the fact that the light is on, doesn't neccesarily mean that it has to be an O2 sensor problem. Lot of other reasons too.
There are 4 O2 sensors on the new trucks.

 

I had an O2 sensor disintegrate after 150,000 miles on an olds toronado. Mileage and performance were horrible. The mixture going into the engine screwed up the MAF sensor and required the entire fuel system to be cleaned.

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'99 Lariat Supercab 4x4 SS
5.4L, 3.73 Diff (9.75" LSD Rear, 8.8" Front)
ORP: Skid Plates, LT265/70R17 GY Wrang. AT/S
Group III towing: HD Electrical/Cooling, GVWR 6500# (Extra leaf spring).
Step Bars
4W Disc anti-lock brakes
K&N filter
Stock Items That Differ Across F150s: Steel Driveshaft, Oil filter bolted to engine w/ drip guard, 4R70W transmission.

 

YEA, what Granpa said. you should get that replaced soon. I know the O2 sensor was A really big problem In the 5.0L/4.0L that they used In the Explorer/Mountaineer/Navajo trio. I had to replace mine In my 92 Mazda Navajo At 39,000 miles and then again at 80,000 miles.(Mazda Navajo is just A 2 door Explorer sport w/ the 4.0L engine)I know countless others with Explores that have had ther O2 sensor replaced also. Some with under 5,000 miles on it! But I have not heared about faulty O2 sensors In the new truck engines, 4.6/5.4/6.8L. Lets keep each other informed...