# EVAP system



## ukrkoz

*Missing fuel cap*
*Defective or damaged fuel cap*
Distorted or damaged Fuel Tank Filler Neck
Torn or punctured Evaporative system hose(s)
Defective Fuel Tank Sending Unit gasket or seal
Split or damaged Carbon Canister
Defective Evaporative Vent Valve and/or Evaporative Purge Valve
Defective or damaged fuel tank
Defective Fuel Tank Pressure Sensor

bad fuel cap is about the most common or most profitable "problem". it's 10 bucks worth repair that can be milked into big bucks easy.

replace your fuel tank cap with known good quality aftermarket one. reset error codes at any parts store. make sure that from that point on, you do click that cap at least several clicks after each refill and do not forget to put it on. do not overfill tank, stop after 2nd shut off.


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## fjacky

I'm gonna drop by the auto wreckers and grab a GM gas cap. 

Thanks, I was just worried about doing further damage


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## itguy08

fjacky said:


> I'm gonna drop by the auto wreckers and grab a GM gas cap.
> 
> Thanks, I was just worried about doing further damage


I don't think I'd do that - it may be leaky too. When I bought my last gas cap it was like $10 at the parts store.


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## ukrkoz

guy, *quality* NEW cap from Autozone, with pressure relief valve, is $6 plus tax. why even think about salvage yard?


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## ukrkoz

oh, and run can of Seafoam through tankful. I have fixed my wife's RX300 cap code with this 3 times already. of course, just jinxed it.


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## ukrkoz

CREDIT TO GMMERLIN:

_The dreaded GAS CAP code!!!

I see many posts here about how to fix ( the dreaded GAS CAP) EVAP codes. Today I am going to educate you as to the functions and diagnostics involved in Evaporative Emissions issues and what the codes mean.
Lets start off with the whys.
The purpose of the Evaporative Emission system is to limit the amount of Hyrdocarbons released into the atsmosphere.
Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid ON, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid OFF, fresh air is drawn through the vent solenoid and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.
So in a nut shell if the control module senses a leak in the system that will allow more than a prescribed amount of fuel vapors escape, the module will illuminate the yellow engine light also know as the Check Engine (CEL)or Service Engine Soon (SES) light. 
Depending on the year, make and model of your vehicle, this leak could be as small as .020” or twenty thousands of an inch ( a hole equal the point of a sharpened pencil lead)

Now with any diagnosis, the first thing we what to do after verifying the concern is to check the codes. This can be done at just about any chain auto parts store or if you own a code scanner, you can do it yourself.
DO NOT CLEAR THE CODE!!!!!!!!!!!!!!!!!!!! This is your key to finding out what is going on……we will clear the code after we repair the vehicle.

EVAP codes are considered either TYPE A or TYPE B codes..which in simple terms means the control module must see 1 failure for a TYPE A or 2 or more back to back failures for a TYPE B before the SES or CEL light is turned on.
Lets take a look at the codes and what they mean
P0440 or a P0455 – This is a Large leak indication or as people call it “The GAS CAP code”
This is a TYPE B code. Usually the code is caused by the gas cap being left off or loose after a refuel. This code could also be caused by any failure of the EVAP system that will cause a large leak.
P0442 – This is a Small leak indication.
This is a TYPE A code. This indicates a leak as small as .020”.
This code needs some serious diagnosis and knowledge of the system to find and repair the leak. Usually specialized equipment will be used to identify the leak.

P0446 – This indicates there is a restriction or blockage of the Vent Solenoid.
This is a TYPE B code. Any thing that prevents the venting of the EVAP system will set this code…usually dust and debris in the Vent solenoid or a damaged vent hose will cause this.

The other EVAP codes (P0443,449 etc) are electrical codes related to various components of the EVAP system.
Electrical codes need some good diagnostic skills, knowledge of the system and some specialized equipment.

With any car repair concern, there is a logical flow to follow when trying to identify what is going on..here in the GM world, we call it Strategy Based Diagnostics or 7 simple steps to diagnose a concern.
As always, verifying the concern and then doing a thorough visual inspection is key. It’s amazing how quickly a problem can be fixed by just the results of a visual inspection.
Now getting back to EVAP concerns….once you have identified the problem, you must come up with a repair, then a verification that the vehicle is repaired properly.
With EVAP leaks, usually a large leak is caused by a loose gas cap. Reinstalling the cap and clearing the code will be a quick remedy. But remember that you must always verify your repair..this could include professional intervention…(EEK!!!!!!!!!PAYING SOMEONE TO WORK ON MY CAR…..NO WAY!) . Well yes, this may be necessary..I have seen many times where people have come in to have a EVAP code cleared and refuse diagnosis only to have the light come back on…then blame me for the light coming back on…(then post on AF how the “stealership” did not fix their car).
But this isn’t a rant, this is information on what is going on.
Repair verification could include EVAP system testing with specialized equipment to verify that there are no leaks present..I personally check every EVAP system for leaks even if I find the customer left the gas cap loose…this insures that there are no other problems with the system that would cause the customer a trip back to see me. Far too many times have I seen someone tighten a gas cap and clear a code only to have the vehicle come back a few days later with a “real” EVAP leak…masked by a loose gas cap.
If you have a SES or CEL light caused by an EVAP concern and you have the code cleared and it comes back on after a few days….get to your local repair shop ( I recommend your local dealer with factory trained technicians) and have the system tested and repaired properly.
If you want to DIY the repairs, feel free, there are plenty of resources on the internet, but just don’t jump in and replace parts…educate yourself on the system and perform some diagnosis…many times a part will not fix the concern…
Good Luck
GMM _


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## fjacky

Gas cap replaced... 2 days later the same code is back. I think I will return the $15 cap and just ignore the code for now.

Would thus code possibly affect mpg?

Thx all


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## Bigplanz

If you live in a location that requires emissions testing, your code will fail your car and you won't be able to register it.


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## ukrkoz

my son's eclipse has CE light for 2 years already, and passed 2 emissions tests. WA state. needs a peice of plastic valve that happens to cost $457 pre-tax. we ain't paying it. still does 32mpg. 
fjacky, you did have code reset, right? and you did run Seafoam through the system right after? 
everyone says mpg drops a little bit. 
i am not sure what car/mpg you do normally have. i'd say, 0.5 mpg probably will come in play. 
inspect cap seat on the tank for any damages. 
otherwise, you'll have to run full blown diagnostic on it and find exactly what is causing the code. and cuz it's EVAP code, it will be repairmen guesswork either.
if you are ticked with that light on the dash, piece of electrician tape covers it well. or picture of significant other. or a pet. amd well aware of several cars that drive with that code around for years. still driving.


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## fjacky

ukrkoz said:


> fjacky, you did have code reset, right? and you did run Seafoam through the system right after?
> g.


i did not run seafoam through it...forgot.

I did look for it though and there was several seafoam versions.

http://www.canadiantire.ca/search/s...>folder_id&FOLDER<>folder_id=1408474396672077

not sure which one i should get


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## ukrkoz

i think it happened 2nd time gas cap code came up on my wife's RX300, when i had to reset code twice. have battery disconnected overnight to really clear it. or, if you can locate ECU fuse, pull it out overnight, so that you do not have to re-set all radio and clock settings.
you want Seafoam motor treatment that is in a white cap bottle. Red cap one is for transmissions and is called Transtune. works very well either for its purpose.
you can not pour it directly into the tank. you will need a narrow funnel to pour it in. best way to do this is to buy it, have funnel handy, get to the point when you have time (weekend?) and tank is needing refill. find a major auto parts store next to freeway and a gas station. drive to parts store, ask them to reset code, or pull fuse out for maybe 20 mins to reset it. then go to gas station, pour Seafoam into tank and FLUSH IN WITH GAS. go on freeway, and go for maybe 30 minutes trying to keep speed at maximum legal level. gets engine real hot and blows Seafoam well through the system. 
if that code still comes back, you will need what is called a leak tester, to determine where leak is coming from.

keep in mind, you did not have that code for 2 days. if it's THERE, it normally comes back in several minutes after reset. hence, we do have at least some positive result from new cap. 
make sure you do not top fuel tank. i do 2nd click and it's enough. trying to top tank can cause gas vapors problems, causing that leak code.


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## fjacky

Thanks for all of the info.

I don't think it's the gas cap as when I cleared the code with my old gas cap it took a couple of days for the code to come back as well. 

I think I'll try the old cap with seafoam and see if it does the trick


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## ukrkoz

hey, what kind of GM vehicle is it? some of them had gas tank intakes reported loose, resulting in that code. apparently, if there's a leak, it is minute and takes time to come back.


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## Bigplanz

That's interesting that Washington will pass a car with a check engine light on. Here, and everywhere else I've ever been or heard of, that's an automatic fail. Guys with old clunkers sometimes clear their code while in line at the testing center, praying it won't come back on while they are getting the test. :laughing:


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## ukrkoz

even if it fails emissions, you can still pay $200 to a shop to do "reasonable repairs", bring slip back to emissions station, and you are good for another 2 years. :thumbsup: old clunkers around here are exempt from emissions anyway. and many of them run better than all those electronics filled tin cans.


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## fjacky

ukrkoz said:


> hey, what kind of GM vehicle is it? some of them had gas tank intakes reported loose, resulting in that code. apparently, if there's a leak, it is minute and takes time to come back.


It's a 2004 cavalier


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## fjacky

ukrkoz said:


> i think it happened 2nd time gas cap code came up on my wife's RX300, when i had to reset code twice. have battery disconnected overnight to really clear it. or, if you can locate ECU fuse, pull it out overnight, so that you do not have to re-set all radio and clock settings.
> you want Seafoam motor treatment that is in a white cap bottle. Red cap one is for transmissions and is called Transtune. works very well either for its purpose.
> you can not pour it directly into the tank. you will need a narrow funnel to pour it in. best way to do this is to buy it, have funnel handy, get to the point when you have time (weekend?) and tank is needing refill. find a major auto parts store next to freeway and a gas station. drive to parts store, ask them to reset code, or pull fuse out for maybe 20 mins to reset it. then go to gas station, pour Seafoam into tank and FLUSH IN WITH GAS. go on freeway, and go for maybe 30 minutes trying to keep speed at maximum legal level. gets engine real hot and blows Seafoam well through the system.
> if that code still comes back, you will need what is called a leak tester, to determine where leak is coming from.
> 
> keep in mind, you did not have that code for 2 days. if it's THERE, it normally comes back in several minutes after reset. hence, we do have at least some positive result from new cap.
> make sure you do not top fuel tank. i do 2nd click and it's enough. trying to top tank can cause gas vapors problems, causing that leak code.


Did all of this and the code came back after 2-3 days. I'm just gonna leave it


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## ukrkoz

yeah, will take specialized equipment to track the source. Cavaliers are not bad cars though... esp with V6 in them. lots of power for the size. 
sorry, simple cures not always work. at least, now you drive a clean fuel system car.


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