Our 97 Blazer has been throwing a code light (not a flashing) for about two months now. I had the code read & it was either a Cat or rear O2 sensor. It would stay on for awhile then go off then return. Well I had a Magnaflow aftermarket Cat installed last week. The OEM Cat was burned up & starting to plug up. But now the light stays on & doesn't go off at all as before.
My question is what goes wrong with an O2 sensor? Do the burn out or get dirty?
Since having the Cat replaced the power & fuel mileage is up. But then again when the light was on before the cat change the mileage was better but worse power.
Anyway just wanted some input before I go buy a sensor. I guess I should get the code checked again before I do anything.

 

yes, I believe they can burn out and get dirty.

 

I took it in this morning to have the codes read. It appears the code is a timing issue. Either mechanical or loose or defective cam or crank sensors. I had a distributor replace a while back so maybe the sensor is defective. I guess it could be the timing chain, but it doesn't act like a loose timing chain. So it is going in tomorrow to be checked. I'm so grateful I'm at a place in life that I can have a lot of my work done. I still like to fool around with some of the repairs.
Thanks for the reply. I wasn't sure if cleaning them was an option or if they just burn out. They are basically just a metal bulb that sense heat.