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2004 Pontiac Sunfire What do these codes mean?

Tiny
JL984
  • MEMBER
  • 2004 PONTIAC SUNFIRE
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 128,650 MILES
I took my car in for a diagnostic test because the check engine light came on. These were the codes that came up P0300 and P0420. I called the dealership to see if my car was still covered under warranty to have the catalytic converter replaced and she told me that it was but that I would have to wait for the engine light to come back on before I should bring it in. I am afraid my car is going to blow up on me or something like that because I have no idea what these codes mean. The guy did not explain it to me although I did not ask. He told me that sunfires are known to have ignition problems and cat problems but nothing more then that. I had the fuel filter, spark plugs and the ignition replaced about a month ago. What is wrong with my car? Or can you at least explain to me what the codes mean?
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Monday, March 31st, 2008 AT 4:44 PM

3 Replies

Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
P0300 is a random miss fire, and that could be caused by your plugged converter causing a high amount of back pressure. They dont need the engine light on to check if the vehicle has a bad convertor.
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Monday, March 31st, 2008 AT 7:50 PM
Tiny
DUMENUF2TALK2U
  • MEMBER
  • 5 POSTS
I'm working on a 03 sunfire and got the same codes. I replaced the upstream O2 sensor and it got rid of the cat code, but I still can't fix the p0300 code
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Wednesday, February 16th, 2011 AT 10:20 PM
Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
Your going to have to figure out why it is miss-firing and if it is indeed actually missfiring and not just an issue with the crank shaft position sensor. Start off with the basics. Tune ups. Things that can affect all the cylinders. Ignition coil, plugs, plug boots, fuel filter, air cleaner, intake leak, and timing
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Saturday, February 19th, 2011 AT 4:43 AM

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