Engine light came on. Help!! - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 7 (permalink) Old 09-19-2018, 06:49 PM Thread Starter
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Unhappy Engine light came on. Help!!

The code I have coming out of it is a P0455 large leak in the fuel Evaporative Emission System. Am I better off just going to a professional to look at it or is it something I can fix. The stuff from my Google search is all over the place.


Thanks in advance.
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post #2 of 7 (permalink) Old 09-19-2018, 07:06 PM
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It could just be the gas cap. Make sure it's tight and replace if tight.

p.s. It's a known problem and the gas cap has a special extended warranty valid for 10 years or 120K miles.
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post #3 of 7 (permalink) Old 09-19-2018, 07:27 PM
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This code is generally caused by 3 things. A gas cap that is not sealing up correctly after its ratcheted on. The purge valve on the engine may not be letting the vacuum get thru it to reach the fuel tank (when its supposed to), to pressurize the fuel tank to a specific vacuum level. Or the canister vent valve is letting the vacuum leak out of the tank instead of trapping it. If the vent line was clogged, that of course would prevent getting the vacuum back to the tank, but I've never read where that was found to be the cause. A plugged vent line from the canister to the vent valve solenoid could be at fault. But most of the time it has been shown to be a faulty canister vent valve solenoid. Removing an reinstalling the gas cap correctly, is the easy stuff. The R&R of the purge valve, is fairly easy. Anything else is a killer an expensive (if done in a shop). If you just got gas (an this is the first time to see this fault code), I think you would have to lean towards the gas cap as a first try chance for a fix.
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post #4 of 7 (permalink) Old 09-19-2018, 09:20 PM Thread Starter
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Thanks. I did check that and the gas cap was lose. Do I need to clear the code or will it clear?
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post #5 of 7 (permalink) Old 09-20-2018, 05:30 AM
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The code will eventually clear on its own, but am unsure how long it takes nor how to expedite the process. By the way, is the lettering on the gas cap white or blue?

#NEVER GIVE UP
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post #6 of 7 (permalink) Old 09-20-2018, 10:36 AM
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With the understanding that the service manual information is correct, you can expect to see this >>>> Any of the many fault codes that are classified as an A or B rated fault, turns on the MIL light. It will remain on until the car has completed 4 *consecutive* start/run cycles without detecting any problems with ANY of the A an B rated items. So if you do something that may/feel corrected the problem, you would have to wait for those 4 run cycles before you would see that light cancel. Or you hookup a scan reader device, an force a reset. That would cancel the light right away.




Added thoughts >>>> I'm thinking that whenever you have a scan/fault reader force a reset, all the monitored emission devices, are forced to start their testing over from scratch. Most are tested an reestablished quickly. But the EVAP portion can take quite a while to get back to its ready status. But since that monitored function happens to be the circuit having the problem here, a reset probably would be the quickest way to see how the system is working now.



Makes me wonder if all of the continuously adjusting functions of the fuel trims an transmission shifting action etc (based on how it senses the driver using the cars gas pedal an trans, so to speak) are also reset to zero an have to start over again after a scan/reader reset command has taken place.

Last edited by GOPHERIT; 09-20-2018 at 01:31 PM. Reason: added thoughts
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post #7 of 7 (permalink) Old 09-20-2018, 09:03 PM Thread Starter
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I did a scan and it is gone. Everything is working well. Thanks for everybody's help with it.

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