Problems/Service/Maintenance Do you have problems with your new 2.0, 2.2, or 2.4L? What kind of service did you have done?

"check gas cap" message, always...

Old 10-26-2018, 10:33 AM
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"check gas cap" message, always...

2006 ss 2.0 sc cobalt, 110 K miles, runs great. but every few days the "check gas cap" text in display comes on, then shortly after the check engine light displays, every time I scan it, it says "large leak p0455 evap system". I check the cap its always tight, I also replaced it, but it does the same. I can clear the code but every few days it comes back on...I understand the whole system of evap but...
looking for specific parts that are the most common to not seal or fail in these Cobalts?
what should be checked and or replaced in what order of most likely to fail and trip this code.

thanks

Last edited by 71jcguy; 10-26-2018 at 10:54 AM.
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Old 10-26-2018, 11:50 AM
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When you are filling the tank (adding gas), does the gas sometimes overflow? Could be a stuck ball check valve in the fill line. Some older Chevy's had this issue and the valve/fill line needs to be replaced.
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Old 10-26-2018, 12:26 PM
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no, no issue filling
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Old 10-26-2018, 02:27 PM
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did you check your EVAP purge solenoid on your engine? its right next to the valve cover. has a line running to the supercharger.
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Old 10-26-2018, 02:28 PM
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Old 10-29-2018, 10:11 AM
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Check the purge valve like leemanfor mentioned. If they fail stuck open then the evap system can't seal and the computer reads it as a large leak.
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Old 10-29-2018, 11:13 AM
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alright I will start with the purge solenoid on the engine, thank you.

I am also looking at replacing the tank filler neck as there is a lot of pitting and rust on this assembly, I suspect possible leaks along this piece, but I find two types of new parts for this, listed one with w/ PZEV (Partial-Zero Emissions Vehicle and one with out, which would be correct?

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Old 10-31-2018, 12:15 PM
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alright I replaced the (engine mounted) purge solenoid, reset and light came back on about 1 hour after driving, "check fuel cap" message followed by check engine light. I reset it and replaced the tank pressure sender (in the canister back by the tank) I reset it , and drove about 1 hour and sure enough the same "check cap" message followed by check engine light. so which part should I check next?

also how can you tell if the car is one with w/ PZEV (Partial-Zero Emissions Vehicle) or one without
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Old 10-31-2018, 05:23 PM
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There is possible a broken line.

No idea on the PZEV determination, but I was under the assumption all the cobalts did a fuel cut during coasting
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Old 11-02-2018, 08:29 AM
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so, when it comes to the tank filler neck assembly, two are available one with w/ PZEV (Partial-Zero Emissions Vehicle) and one without.
how can one tell which version they have/need?
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Old 11-13-2018, 02:45 PM
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no leaks found in the lines, and all sensors have been replaced,, but still message displays, so replacing the tank filler neck assembly.
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Old 12-17-2018, 02:48 PM
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finally just received the new tank neck assembly.....so now in the process of replacing this neck assembly, the original was very rusty, thin and able to "crunch" it with my hand. have no doubt it was allowing a leak somewhere..hoping this will eliminate this "leak"
at the same time I'm replacing rad, ac condenser and heat exchanger as they all were pushed back and bent badly. I think some one plowed snow with this car...
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Old 12-22-2018, 08:20 PM
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Did your car smell like gas too? I'm getting this message and some fuel fumes when driving and when the car is parked.

Keep us posted.
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Old 01-18-2019, 03:58 PM
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no smell of gas ever., even when I would sniff around under nether, but always that message every few miles, so capped off the tank spout with a solid rubber cap, sealed it with a clamp and reset light, and just a few miles later, check fuel cap message again. so replacing spout assembly, due to other things found I am also replacing rad, intercooler, pump, and ac condenser. well see if the message comes back after that. if it does I guess next would be to replace the entire canister assembly.
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Old 03-23-2019, 03:08 AM
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Originally Posted by 71jcguy View Post
2006 ss 2.0 sc cobalt, 110 K miles, runs great. but every few days the "check gas cap" text in display comes on, then shortly after the check engine light displays, every time I scan it, it says "large leak p0455 evap system". I check the cap its always tight, I also replaced it, but it does the same. I can clear the code but every few days it comes back on...I understand the whole system of evap but...
looking for specific parts that are the most common to not seal or fail in these Cobalts?
what should be checked and or replaced in what order of most likely to fail and trip this code.

thanks

i read through the whole thread and im not sure if Iím late on helping or if I missed it being mentioned. But the map sensor on the evap unit by the tank could be a failed piece. Potential that the wires have damage and make intermittent signals which should be another dtc but something to check if itís still a problem
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