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P0202, P0204, P0300 2004 Grand Prix N/A *Need Help*



If the light is flashing, it means it is misfiring at that moment. My clogged cat caused a P0300 code, but the light never flashed
 
Last edited:
tomtom123 said:
If the light is flashing, it means it is misfiring at that moment. My clogged cat caused a P0300 code, but the light never flashed
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I never had a chance to pull the O2 today to see if that was the problem. What else are likely common causes of a flash MIL with P0300?
 




As I said, personally when my cat was clogged it didn't blink the SES light, just through the P0300. The reason I recommend the .05 gap is because some cars don't like the gap much larger. But if you had no problems with that gap before, then it shouldn't necessarily be different now.
ICM could be losing connection when warmed up? Other than that, I can't think of anything off the top of my head
 
But also, if you have an extremely plugged cat, it may cause the MIL to flash. I just think you would have noticed a powerloss and P0300 code well before the point where it would make the MIL flash. I could be wrong though.

As Highoctane said, clean contact points on the ICM. Might help. My ICM had quite a bit of corrision on it a while back when I cleaned mine
 
Okay thanks. I will try cleaning that to see if it changes. The P0300 hasn't been on very long. It all started with the combination of the p0202 and p0204 codes. Those codes have since gone away since I fixed that wiring that I found at the PCM harness.
 
now that it runs and drives.....how does it sound when floored, healthy? or like its trying to go but cant get the f out of its own way?

being its dark out, take it for a spin, drive it kinda hard for a bit, then pull over in a dark area and look under the car, look to see if the cat is glowing red. if its red, its clogged up for sure.
 


Scottydoggs said:
now that it runs and drives.....how does it sound when floored, healthy? or like its trying to go but cant get the f out of its own way?

being its dark out, take it for a spin, drive it kinda hard for a bit, then pull over in a dark area and look under the car, look to see if the cat is glowing red. if its red, its clogged up for sure.
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Well I took it out for a drive for the first time since I repaired the wiring. It idled really badly at first but let up a little bit when I started driving. Within a few minutes it started driving better and then after I floored it to get it to rev to higher RPM it stopped stumbling. I came to a stop at a stop sign and the idle was good. I floored it off the start and got to 60mph and it was running great and the check engine light stopped flashing. Got on a stretch of highway and all was good. I cleared the code while driving and drove for a few miles. I pulled over on the side of the road and got out. Engine sounded good and was not stumbling at all with no black smoke coming out of the exhaust. I then turned around and drove it home. I let it sit for about an hour and then took it to dinner (25 mile round trip). No issues, no problems, sounds great, and no more engine light.

I'm guessing that since I didn't drive it after having the PCM wire repair it didn't have a chance to reset fuel trims. Driving it did. So far so good.
 
thats possible, or a chuck of cat that was blocking the exhaust fell out of the way. only time will tell. lets hope im wrong.
 
Scottydoggs said:
thats possible, or a chuck of cat that was blocking the exhaust fell out of the way. only time will tell. lets hope im wrong.
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Lol. I have no problem replacing the cat down the road if need be. I'm just glad that its running good now. I appreciate all of your help.
 
no problem.

should it act up again take a hammer to the cat, when they break up and clog the hammer makes the clog move and clears the pipe.
 
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