I posted this in the CTS section awhile ago but haven't gotten any answers so I thought I'd post it here.

I have an 04 CTS 3.2L 5sp. It has around 107,000 mi. I started having codes thrown about 2 months ago and I finally got around to change sensors. I had a P0138 so I changed Bank1 sensor 2. Then about 3 days later I had P0153 so I changed Bank 2 Sensor 1. 3 days later I got the same P0153 so I removed sensor and took back under warranty and replaced sensor again. 1 day goes by and I get code P2099. I wouldn't even know where to start to look for fuel trim system problems. Weird thing is every time the car throws a code it's always when the car is between 30 - 35mph and in 3rd gear. ANY help would be greatly appreciated. I might have to bite the bullet and take it to the shop, but I would prefer not to, I like to be able to fix these things myself.

So to recap, I've changed the 02 sensors on Bank1 #2 and Bank 2 on #1 & #2.
I am running a K & N air filter on this car. Is this not a good thing?
I did clean the MAF to make sure there wasn't any dirt or oil on it.

Do you think The Cat on Bank 2 is shot? How can I test this?

Thanks again

 

This problem has been resolved: The LT side exhaust flange was leaking.