I am getting 2 different codes

I am getting a P0420 & P0401. The check engine light has come on. I just had the oxygen sensor, bank 1 replaced. What is causing these issues and how do I get it fixed?

 

Did you cleared the code after replacing the parts?

 

Yes, I did. It stayed off for about 25 miles but came back on.

 

Google says 420 is related to cat efficiency. Sometimes the sensor solves it, sometimes the actual cat is the problem.

The big Q around here seems to relate to the brand of the sensor used. Apparently Toyotas don't respond well to many aftermarket brands. So, you say you 'had' it done. Why did you have it done (same code?) and what product was used?

401 relates to the EGR component(s). Could be simple as a vacuum hose, passages coked up or a failed EGR. You need someone with experience working on this (actually both) for you.

https://www.yourmechanic.com/articl...recirculation-flow-malfunction-by-jay-safford

 

If this is referring to the upstream sensor, the one before your CATs on the exhaust, I would ask why that one? It has nothing to do with either code you listed.

 

I had a different code when I had it replaced. Once it was fixed all was good for several months. Then I had my compressor replaced because my A/c wouldn't work. These other codes came up after the compressor was replaced.

 

I'm inclined to say that these things can be normal maintenance items. How many miles are on the rig?

 

Only 288k. I have had regular oil, fluid, and filter changes most of the time before they are required or due. The belts were changed out all the way around when they started squeaking later part of last year or first part of this year. I keep it tuned too

 

All great stuff. But unrelated to preventing the parts failures that are creating your codes.

23 years and 288k miles are good reasons for components to age out.

 

So, what should I tell the mechanic that needs checking? Where to start?

 

If you have to tell the mechanic where to start, you're using the wrong mechanic.

He should have available diagnostic trees that guide him for the solutions to the codes set.

If you read down into the link given in post 4, you'll find that you might be able to address the EGR yourself. Could just be a broken vacuum line.