p0420 help

[FinalBreath05]

New member here. 03 Yukon XL Denali. I've got a P0420 and I also get a flashing cel anything above 2400 RPM's. I've replaced plugs, wires, coil packs, cam sensor. Cleaned MAF sensor. Replaced all my exhaust manifold bolts. I had 3 broken on each side. Any help would be appreciated.

 

[Scottydoggs]

thats the old bad cats code. they need to be replaced.

 

[PG01]

http://www.bigdaddiesgarage.com/mini-cat-cel-fix.html

https://www.obd-codes.com/p0420

 

[Rocket Man]

I agree, the cats are probably plugged. That's why the cel is flashing too. Don't continue to drive it with the light flashing or you will do serious damage.

 

[swathdiver]

Did you do all that stuff because of the P0420?

 

[FinalBreath05]

The only thing I replaced because of the code was the cam sensor. The rest was just a tune up. Truck has 330k on it. I've been driving it the better part of a year with the CEL on and I just keep it out of the RPM range where it'll flash. I've got a scanner but haven't hooked it up yet. I replaced the exhaust manifold bolts because it was leaking and sounded like crap.

 

[swathdiver]

Ok, well Matthew, a P0420 has nothing to do with a camshaft sensor. That's the driver's side cat all day long. I've been having the other one act up on me for about six months now and just the other day the driver's side threw a code. Lord willing, they'll be in the trash later this week.

After you pull the codes share them with us and we'll do our best to help you out. It's cool to see trucks with that kind of mileage still on the road. Came across an old-timer a month or so ago with an old Yukon with the body and interior near immaculate with that many miles and it sounded just fine too.

 

[FinalBreath05]

Ok, well Matthew, a P0420 has nothing to do with a camshaft sensor. That's the driver's side cat all day long. I've been having the other one act up on me for about six months now and just the other day the driver's side threw a code. Lord willing, they'll be in the trash later this week.

After you pull the codes share them with us and we'll do our best to help you out. It's cool to see trucks with that kind of mileage still on the road. Came across an old-timer a month or so ago with an old Yukon with the body and interior near immaculate with that many miles and it sounded just fine too.

I replaced the cam sensor because of the Flashing CEL. This was a retired gentleman and him and his wife traveled a lot. Trucks in immaculate shape. I couldn't pass it up. Only two codes I have is P0420 and a P0300

 

[swathdiver]

The latter code is generic, so take care of the cats first. Here's your chance to get long tube headers and a catless y-pipe for $200 if you don't have to worry about emissions testing.

 

[Rocket Man]

The P0300, multiple random misfires, is probably because of the cats too. If the engine can't breathe it can misfire like that. I'm sure you notice it if you try to get it above that 2400 RPM, and if you continue to push on the gas it will buck and misfire badly. That's ******* your engine even at lower RPM's.