Picked up an obd 1 code reader today and pulled codes on my 1992 f150. Got 41 for O2 sensor. I already guessed it was bad because it was rusted and my bad mpg. Pricing O2 sensor at autozone down the street, they asked whether it was downstream or upstream O2 sensor.
Do I need to replace both, and where is the 'upstream' sensor?

 

I just replaced my o2 sensor on my truck (obd1) and I only have one sensor, its located in the center of the exhaust y pipe. I ordered mine off rockauto and I never saw anything about upstream or downstream so I really couldn't point you in the right direction there

 

Yea I havent heard of it either but three of the seemed to think there is one.
I found the sensor on amazon for half of what they wanted, including feee shippng. I dont see how they can have a 200% markup

 

Just part of the business, gota make money some how I guess. I went to my local auto parts store for an engine coolant temp sensor and they said it was 50!!! Went online and got one for 16 with shipping. It is nice to walk out of the store with the part but its worth the wait to save that much money

 

Upstream o2 sensores are before the cat, down stream is after.my truck has them, even with my aftermarket exhaust.

 

That makes sense. Thanks for telling us that

 

No problemo!

 

A bad MAP sensor or a vacuum leak will also throw a code 41.

 

And a 92 will only have one sensor.