I get a different code about 1 ever 3 months.

CEL came on this morning, just had it checked,

P0300, and P0420

Car has had a High Flow cat/Vibrant header since March. First time I've seen the P0420.

Ideas?

 

No one on this site probably will never help u because thats what ive noticed but the P0300 code i had and changed the plugs and it went away. Its a misfire code

 

What plugs did you put in it? I put in new plugs bout a month and a half ago. Had the problem, before and after.

 

Colder plugs? What kind? Did you gap them?

 

It had the NGK BKR&E plugs, and when i went to replace them, i couldn't find them so i got some autolite iridiums. Guy said they were pre gapped??? may be my problem, may be the plugs themselves.

 

So, its been raining all day, and I've put about 100 miles on the car in the rain. ODDLY enough, check engine light just went off and hasn't been back on since??????

 

As my buddy says, when it comes to Cobalts and engine codes it's like playing pokemon. You gotta collect em all lol

 

p0420 is from "catalytic efficiency below threshold" aka, you have an aftermarket exhaust and the 2nd 02 sensor is throwing a code, or your stock cat if you have it is shot. get a new cat, or get the code deleted using HPTuners.

the other is a misfire code the above poster is correct, make sure your plugs are gapped properly. google "proper spark gap" and there are tutorials for gapping non-OEM plugs to get em to work properly. if it's brown and dirty, the gap is too small, if it's white it's too big.

 

Its got a high flow cat, thats only been on since March?

 

So the CEL came back on early this week.(After the car sat for two days). And Once again, its been raining all day here in NC, and I went and drove the car, and sure enough, the CEL went back off. What does rain/wet have to do with me CEL going off?

 

don't think the rain has anything to do with it but i've been clearing that p0420 code out on mine since i've had it

 

what kind of air intake or filter do you have. may be getting water in and causing your misfire which will throw out you 02 sensor causing its code so if you can fix your misfire you should fix that as long as it worked with your high flow before. i had to replace and use a smaller gap recently on my plugs due to a misfire issue and it sounds just like what you have wrong

 

I've got an Injen Cold Air Intake. Not sure which filter, its dark redish, with a wire mesh type thing built in it. To me, its location is horrible right in front of the tire, I dont see how it doesnt suck up water, with the plastic shield thing being the only thing to block the water.

 

ya i'd get the hydro sheid too and get your plugs sorted out. good luck