The check engine light came on and I had it read. they said it was the O2 sensor. They recommended that I replace it, but a couple of days ago the light went off and the gas mileage went back to were it was. What is going on? Has anyone else came across this?

Steve

 

O2s will come and go. I've reset one a dozen times over 3 years and it is still working 99.5% of the time. The sensor doesn't necessarily fail... as in stop... it just starts sending wrong readings, thus tripping the Check Engine Light CEL. Buildup on it, etc usually is the leading factor.

it is not a hard job to replace. Just figure out which one it is. Some Ds have 2 O2s and some have 4. Ouch!

IndyDurango

 

im pretty sure its the 4.7s that have 4 (one for each bank of cylinders )

but they will come and go could be junk on the sensor in the pipe, could be water got into the wires if the light is staying off dont worry about it

 

4.7L do have 4 sensors. 5.9L and 5.2L have 2 sensors.

 

I seem to remember reading somewhere.........oh yeah!! It was this forum........that the 4.7 has 4 sensors, 2 per bank one before the cat converter (UPSTREAM) and one aft of the converter (DOWNSTREAM) the two upstream converters are the ones that are used for emissions, and the downstream ones are basically back up.

+2 Indy on checking which sensor. I would guess that if you had a just sensor fail code, see if there is anything to indicate UPSTREAM or DOWNSTREAM. There is a 1 in 4 chance but I would venture to say that if it comes up with a hard code, then I would probably guess the UPSTREAM sensors first, since that should have most of the buildup on them.