No symptoms, drives fine, don't smell anything weird, no weird sounds, and no puddles on the ground. Vehicle is regularly maintained.

The weirdest thing is it'll come on after 1 or 2 days of driving after having unplugged the battery (reset ecu) and then it'll switch itself off 1 or 2 days later.

Any ideas what this could be? It's been doing this for a couple months now and it hasn't really worried me enough to take it in. I have a suspicion it might be the O2 but I'm really not sure.

 

It's possible that the O2 may be going but you might want to get the codes read anyway because sometimes there are "pending" codes (meaning no CEL but the ECU is logging them). Other than that you need to catch it when it actually throws the code(s) and before the ECU clears them.

 

Cool, thanks for the info. Guess it's as good a reason as any to start saving for an auterra.

 

try cleaning the maf sensor then go from there

 

He's got a 97, it's alot more rare to have issues with the MAF being dirty on a 96-98 than it is on a 99-02.
The O2 sensor would be a good guess, but again it's just a guess without having any OBD codes.

 

The great thing about OBD is it tells you what to check out with the code. So first step is to read the code.

 

Is there any reason to ever replace the rear o2 sensor if it isn't broke? As I understand it, it only tells the ecu that the cat is actually doing it's job. Whether or not it's working at peak efficiency shouldn't really matter right?

 

Correct, only reason to replace it would be to get rid of a CEL.