Code P0420

My 2004 TRD OR 3.4 260K miles CEL code P0420, I cleared it 300 miles ago and it still hasn’t come back. Should I be concerned?

 

Check for exhaust leak, most common

 

Thanks

 

It will come back. When you force clear a code it resets the emissions monitors to clear them. Once your truck completes (or tries to complete) the next emissions cycle it will return. That code comes and goes until eventually it just stays on. Most likely you need new catalytic converter(s) or have an exhaust leak. With trucks this old and high mileage it could be either or both, gotta do some digging to find out.

 

Thanks for the fast response! I have noticed what sounds like an exhaust leak coming from the left side of the engine I guess I need to see if I have a cracked manifold or just loose exhaust pipe connector.

It’s not a bad leak just slightly noticeable.

 

I had to replace most of the exhaust gaskets around 150k cause they were leaking out of the unions in the exhaust system. I was lucky enough to take my time and not break any studs when doing the work, but it's one of those jobs where you are constantly one bad move away from a huge ordeal.

 

I live in the South so my truck is not rusted any more than expected I will hit them with penetrating oil and hope for the best.

Thank you very much!

 

Another vote for it likely being an exhaust leak. Was the case for me, between rear CAT and rear O2 sensor.

 

Did you have to replace a gasket or just tighten it up?

 

worth a read

https://www.tacomaworld.com/threads/addressing-some-common-misnomers-of-the-p0420-code.396763/

 

The leak was from rust and the original gasket/mount was long gone by that point so I had someone just weld up where it leaked and that fixed it.