Check engine light came on. OBD reader at O'Reilly's showed either an O2 sensor or a catalytic converter. Any advice where to start first? The truck idles and runs perfect.

 

Are we supposed to guess what you're working on or what the ACTUAL CODES were?

 

97 4.6

 

Read and answer the WHOLE question.

 

Without much information to go on, I sounds like (P0420 Catalyst System Efficiency Below Threshold bank 1) or the P0430, same for bank 2.

I had the P0430 on my 97 XL 4.6, and when cleared, it would return roughly every 100 miles or so. Searching this forum, came up with replace CAT or the O2 sensor. I was going to buy a replacement CAT but would put it off as I wasn't sure if the engine had a problem and replacing the CAT would just be a temporary fix. I finally pulled the rear O2 sensors cleaned them off and swapped them (driver and passenger side). So far 600 miles later, I have not had the P0430 code.

So, this forum has a plethora of information and many helpful people, but full disclosure of vehicle and symptoms with codes are a must.

 

Sorry I didn't give enough information. The guy didn't share the codes with me.

 

Try a bottle of cataclean.. Cleared my check engine light for the 02 code

 

Unless you want nothing but guesses, you'll need to go back and get them

 

I got the same error. Replaced all 4 sensors to be safe. Light came back shortly after. Cats were bad. Picked up Spark Plug Non-Foulers for $5 to bypass the O2 sensor so that I could pass emissions. Not worried about cat efficiency on my particular truck (non-daily).

 

Anytime you have codes read make sure they give you the actual codes and post those here, not what they think they mean, which is often wrong.