I have code P0171 P0300 and P0420
Ok so my engine light came on and my car is now running really bad. It has terrible acceleration but once in am at full speed it is fine. I have a 2006 Pontiac G6 with the 2.4L with 61k miles on it. I am out of warranty except for the Catalytic Converter and the PCM. I really want to trouble shoot this first before I have to bring it to the dealer if it is a converter problem. I took my car to my friends shop to get the code out of it to see what we can do.
P0171 is that the engine is running lean
P0300 is a misfire in two cylinders. (Car does not sound like it is misfiring)
P0420 is Catalyst System Efficiency Below Threshold which means that the Cat converter is not working so great.
I have been doing research on this and other sites say that you need to fix the first codes before you fix the 420 code. The first codes could be causing the 420 to come on. I was also reading that a vacuum leak could cause the misfiring.
I really think it is the Converter the car was making a rattling noise from the exhaust when i started it up in the morning. The noise went away the same day the engine light came on.
Has anyone else had this type of problem? Any help would be appreciated.