420 code

[Oldman]

Got an '01 SSEi that's throwing a 420 code. Never seen this one before and searching the site for it showed no results.
It's skipping on heavy acceleration and have not been able to figure out why. Hopefully this new code could help me figure out the problem.

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

I get an occasional code telling me of a lean condition on bank 1, and have not found the reason for this either. The lean condition code popped up occasionally when the thing was running perfectly, so I just ignored it.
Any help on this would be greatly appreciated. Thanks,

[jshow816]

It's most likely a bad catalytic converter. When I had that code I bought this converter from amazon and had it welded on at a local exhaust shop. The shop did the install for free since I let them keep the old core. The old converter is worth around $100 at my local metal scrappers.

http://www.amazon.com/gp/product/B001HM ... ge_o01_s00

The code has not come back since I had the converter replaced.

[AJT2004]

I also had a "intermediate lean condition condition on bank one" which turned out to be a slight vacuum leak. The hose connection had a split on the underside making it hard to find.

[Oldman]

Thanks guys. My cat was gutted about 5 years ago. It's just an empty shell now. All vacuum lines have been replaced, that's not it either. I've been reading a little on this and think it might be the EGR tube. I "smoked" the engine about a year ago and remember now that there was a very slight leak where the EGR tube comes out of the intake. I'll replace that and see what happens.
Thanks,

[nos4blood70]

That code usually pops up if you gut the cat. Are you tuned?

[Oldman]

"Tuned"??
No idea what you're asking. Again, the cat was gutted 5 years ago and this week is the first time the code has appeared.

[1oldman]

a bit of levity here, but are you sure you don't need to move to Colorado, Washington State, New Mexico, or California? - BC

[MKMike]

Is it possible that the cat never actually was gutted?
I ask because you are having trouble under acceleration and also because the code never appeared until now.
Normally I would suspect that the catalyst was restricting the exhaust flow.
Here is how to troubleshoot that code:
http://troubleshootmyvehicle.com/gm/3.8 ... 420-page-1

Often the P0420 problem is one or both oxygen sensors.
Oxygen sensors are actually considered a maintenance item with replacement recommended at 100K miles on OBD II cars.

[Oldman]

Thanks for the link!
I gutted the cat myself. Was told that performance and MPG would improve. Yeah, we all make mistakes! It was over 5 years ago and I drilled a hole through it and then used a piece of pipe and beat all the insides out! Never realized that all that stuff that I swept up and threw in the trash had some value to it! I've had some skipping and shuddering on hard acceleration. Is it possible that an ignition problem is causing incomplete fuel burn and a very rich exhaust, and this is what is causing this code?
I'm sure I need to change plugs and wires and go from there to fix the misfires and skipping. I've been working very long hours lately and have honestly just not had the time to do the simple stuff that I know needs to be done.
Thanks,

[Oldman]

Update: I've now resolved the shuttering on acceleration problem. I had purchased a coil a few months ago and when this started, I got a ICM and two coils from a U-Pull yard. When I still had the problem, I eventually discovered that the coil I purchased a few months ago was the problem.
Anyway, car is running great, but one day I'll get a P0171 code and the next day I'll get a P0420 code.
About 5 years ago, I beat all the insides out of the cat, so it's just hollow on the inside. Don't know why, but these two codes are very recent.
Will these codes cause the "brain" of the car to make adjustments? Will the presence of these codes cause the car to run lean or rich to try to resolve the problem?
I'm not worried about seeing the codes, but I don't want to damage anything and I don't want to reduce my MPG's either.
Thanks,

[MKMike]

Both codes will result when the engine is running lean.
Clogged fuel filter, vacuum leak, dirty MAF sensor, faulty 02 sensor, failing fuel pump and a bad PCV are all possible causes.