Hi All,
I have been away for awhile but now have an '02 4cylinder, 5 speed Ranger.

I got a CEL and had Autozone pull the codes which indicated an upstream 02 sensor. I replaced the sensor and canceled the CEL. After about 4-5 starts the CEL came back on with the same code. Cancelled again and again after 4-5 starts CEL is back on. Indication is 02 sensor.

I suppose it is possible that the new 02 sensor is bad but what else should I be checking?

 

These are heated 02 sensors. Ensure fuse 15 in the under hood fuse panel is good.

 

what was the actual code #....................let me guess p0171?

 

I can't find the code slip but I believe it was Po 171.

 

A p0171 by itself is the O2 sensor doing it s job and reporting that you have a lean condition. Most of the time it is a vacuum leak or a fuel pressure issue.......in your case suspect a vacuum leak.......I think on your engine there is a common vacuum or pcv hose that cracks...do a search or look around your engine for a bad hose...........next time you have an issue don't listen to AZ people ..most don't know what they are doing or they want to sell you parts..........post the issue here first.

 

Yep, unfortunately once again someone who didn't know that the P0171 code is not an O2 sensor code listened to the non-mechanic ignorant working at the parts store who would love to sell you an O2 sensor and make a commission on it. They are great for access to their code reader, but they often no next to nothing about cars.

Again, thats why you are a member of an automotive forum, there is a wealth of information here, and a lot of people who have had the same problem as you and know how to fix it.

Vacuum leak is the most common cause of that code. Usually the PCV elbow cracks and leaks, though any vacuum line can be the culprit. It is possible for the intake manifold gasket to shrink and harden over time which can also cause leaks. If you don't find any broken of disconnected hoses, then you can put the intake gaskets on the suspect list. If the fuel filter gets plugged or the pump gets weak, you will often loose power when accelerating and the symptoms of that are quite different from vacuum leaks. Still if you haven't replaced the fuel filter recently, consider doing so.