P0420 Code

[RaHCon]

New to the site. I have a 1999 K1500 5.7l Suburban with 193K on it. I drove to Denver two weeks ago. SES light came on once we got to Denver. Had local dealer read the code, kiss off $100, and it was "P0420 bank 1". They wanted $1350 to put new cats on. Didn't have them do and drove back to DFW. Light still on. Had AutoZone read the codes early last week and it was still throwing P0420's.

 

I did a little work on it this last week. Cleaned K&N and MAS. SES was still on.

 

Started truck this morning, day after order new cats, and the light is now off.

 

Plan to have AutoZone read the codes again, but trying to decide what is going on.

 

The truck is running great. Good pickup. Smooth Idle.

 

Any Ideas? I would not think that the change in Altitude would cause SES and Cat codes, but I'm not sure.

 

Thanks for any ideas/help you can give.

RaH

[Mike G]

You could have been running a little on the rich side and tossed the codes. A fresh filter will fix the air restrictions for sure. Did you order up a set of low restriction cats? May want to toss them on anyway...

 

--Mike

[RaHCon]

You could have been running a little on the rich side and tossed the codes.  A fresh filter will fix the air restrictions for sure.  Did you order up a set of low restriction cats?  May want to toss them on anyway...

 

--Mike

 

<{POST_SNAPBACK}>

 

 

 

I did order new cats, but am thinking that they are not needed. Since cleaning air filter and MAS, the SES has shut off. AutoZone is still reading P0420, but I think that is left over from when SES was on.

 

One thing I forgot. When I cleaned air filter and MAS, I added 1/3 a can of SeaFoam to 1/4 tank of gas. 2 days later SES shuts off.

 

I am thinking of doing the topend with SeaFoam later this week.

 

I am leaning towards change in elevation causing SES and P0420, but I have very little knowledge in this area. Don't know if it could have be "Bad/Different" gas. Just don't know anything about this stuff.

[71GMC_3/4T]

My buddy got a check engine light on his Trailblazer after a road trip. He went from Denver to back east somewhere, and when he was almost back to Denver it threw the code. He figured the computer was compensating for the change in altitude and either overcorrected or was slow doing it. The light went out after a while, and hasn't had any issues since.

 

Keep driving it and see if it comes back.

[RaHCon]

Thanks for the info. I am going to keep driving it. I do not have to get it inspected til Sept, so if it keeps running like it is I see no reason to change the cats.

 

Thanks again