Alright so I have been getting p0420 codes on and off for at least 6 months. Figured it was the downstream o2 so i either cleared it or just waited for it to clear its self.

Now I am starting to have some bad running problems. I'm not sure how GM systems are set up so idk if they are related.
First problem started a few weeks ago and doesn't happen that often.
When on the highway between 50 and 60 mph with light excl. it feels like my TCC is sticking on and off. The starts to jerk a little, but as soon as i let off and give it a about 50 to 60% throttle it will even out.

Now the last couple of days I have been having some real bad problems.
After the car is warm, it will jerk a lot during excl. To me it feels like either the trans is slipping or the engine is not getting enough gas/air.

Also, after the car is warm, at idle the rpms will drop suddenly and then raise to around 1500 to 1800. Then smooth out. This also seems like the engine is not getting enough air or gas.

The only DTC is the P0420. Nothing for MAF or trans related problems. Like I said, I dont know how GM's systems work. I am Chrysler tech so if these problems can be related to the cat or 02 sensors it would be a great help to know.

 

Have you checked the cat or 02 sensors to rule them out?

 

P0420 points to the Cat I believe. When mine went out, it made the transmission feel like it was going to fall out of the car. Car didn't have any power, transmission was slipping and whining. How many miles do you have on the car? The Cat's on our cars have a recall on them for getting clogged up. They should replace it for free up till about 80-85k miles I believe.

 

x2 on the cat.

 

I think they extended it up to 120K miles free replacement

 

My car has has 141k on it. but i am going to call a dealer anyway and see. Thx.