Evap code

eddieguy

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#1
Make
Chevy
Model
Malibu max LS V6
Year
2005
Miles
155,500
Engine
3.5
Check engine light came on and I had an auto parts store scan for codes and a code came up for an evap code. ( Don't recall code number but would probably know it if I seen it again) then some days later a message came up on my dash that read check gas cap. I'm wanting to know if there is a problem with the gas cap itself or if there is some problem with the way it's put on.
 

nickb2

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#2
Actually, there is no way the car can actually know if the gas cap is defective or badly installed. It's just gm's way of saying "hey" I have an evap leak. It will either light a gas cap light or in your case, message center will say to check gas cap and check engine light will come on. Should be tightened to three clicks. Probably is written that on gas cap.

One thing you can do though is check the surface of filler tube where the rubber o-ring of gas cap mates to the filler tube. If you see rust there, clean that off with some emory cloth. Also check the o-ring/gasket for pitting if the tube is in fact rusted. The o-ring can be replaced, but better to replace the cap altogether. They are relatively cheap.

But this does not mean the code will go away if you have a canister problem, stuck evap purge solenoid, or a crack in evap tubing etc.

If no rust is present, and a new gas cap does not help, best bet is to get it checked out with a smoke machine. If the gas cap is still original, the bet on a gas cap fixing the problem is not a monetary conundrum. It is nowadays almost a maintenance item. A gas cap for your car is about 10-20$. That`s the price of a pack of smokes or a 12 pack of beer. But make sure the surface of the filler tube is pristine and smooth. If it is too rusted out, you may have to change the whole filler tube assembly.

I am seeing more and more in maintenance schedules to check or replace gas cap at x intervals in some manufactures.

Here is an example of what I mean. rust filler tube.jpg
 
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nickb2

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#3
Here is a picture of a monte carlo tube, 2000-2007. Yours is very similar. They rust, nothing to do but swap a new one in.

So remove any plastic covering the filler tube in wheel well. If it looks anything like this, don`t even bother looking eleswhere, this is very common on these gm models. monte carlo tube.jpg

Usually, they leak at weld points for attachment to frame or where tank vent tube meets filler tube. Some ppl try to cheap out and sandblast and epoxy, my opinion is the time and effort are not worth it.

I see rock auto has one for 25-35$. Sprectra is more expensive, depends on how long you want to keep the car. Book time is 0.6hr. But that is on a lift and with a close to empty tank. So run the car to at least below 1/4 tank to avoid spillage before replacing. It should take about 1hr in your drive way. Be sure to also by new hose clamps. Oh, and a new gas cap. ;)

But if you dont see any rust on that tube anywhere, and a new cap doesn`t fix the leak, I will repeat myself, you will need to get it evap tested
Screenshot (306).png Screenshot (307).png
 
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nickb2

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#4
Don't ask me why same part # on same site has a 10$ difference. Mind you, my links are in canadian dollars, maybe it even cheaper in USA $. Usually is.

Anyway, hope this gets you on to a starting point to these pesky evap codes. Sometimes, they are very hard to find, even for a pro.

BTW, happy new year Eddieguy.

Oh, and scratch my comment on tank vent tube, the tank does not vent through the filler tube, the tanks breaths in a different manner when filling it up.

Replacing the tube is very straight forward. Remove three screws at fuel trap, one bolt at frame, remove clamp at tank. Presto. Obviously, tire needs to be removed. I do these in my sleep because of all the salt we put on our roads. On my hoist, I destroy book times and do them in 10-15mins if tank is low. But if I have to empty it, sure, it takes longer. Screenshot (308).png Screenshot (309).png
 
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#5
burred deep in computer logic and trying to simplify EVAP codes the check gas cap message comes about.
The full list of EVAP codes are referred to as 'gas cap' as the parts pushers were fast to recommend a gas cap replacement fix.
Publics dumming down happy to dismiss ANY code as unnecessary emissions BS.
And the PCM is a thinking (fuzzy logic) there was NO issue, vehicle off, fuel level changed, vehicle ON and a EVAP issue lets be helpful and tell joe sausage to check gas cap.


referance P0457-LOOSE FUEL FILL CAP
 

nickb2

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#6
And the PCM is a thinking (fuzzy logic) there was NO issue, vehicle off, fuel level changed, vehicle ON and a EVAP issue lets be helpful and tell joe sausage to check gas cap.
Yup, that sums it up real fast. I almost spit my coffee when I read "joe sausage". :coffee::D

This is where readiness monitors and some cheap 15$ elm 327 shines with a smart phone app.

A visual inspection as I wrote above of anything obvious is easy to do.

But with a elm 327 dongle, you can clean gas cap o-ring or replace it if you suspect it, or just plain put in a new one (cap I mean). There is a calibrated valve in there that fails after time. There are tools to check that, but they are not readily sold to "joe sausage" and no reasonable do it yourselfer would invest in a kit. The tool kind of looks like a rad cap pressure tester. So, like I said, real cheap to try a new one, but chances are real slim it will actually fix the problem. It is hit or miss. But, again, I am repeating myself. Its real cheap, and if you have a 20% chance of fixing the leak, worth a try. But if there is any rust or minute perforation, they must be replaced.

Then erase the code with said dongle, drive it till the evap readiness monitor either passes or fails. If it fails, then you need a bi directional scanner to do testing of various evap solenoids and LDP's (leak detection pump) if equipped. If those pass, then a smoke machine is then your next thing to do. A purge valve may respond, but it may be stuck open for example. ECM won't see that. It will only report it is actuating. Again, not a cheap tool to buy. Never heard of a autozone or canadian tire that rents a gas cap checker or smoke machine or a bi directional scanner.

Problem is, evap codes are hard codes and do NOT go away until some one erases them. So if ignored and driving with check engine light on, one might say to himself, ah, it's just a BS evap code as Kev aptly wrote. But if you do drive with that on, or pull check engine light bulb, or stick a happy face sticker on it, you will not know if the check engine is reporting something else, such as a misfire, cat codes, vvt codes or trans codes etc.

So one may think the car is fine, just emission BS, but you may be killing a major component and not know it.

I am a tech, my check engine light is always on because I have a small evap leak. But I periodically check the codes anyway, just to make sure nothing else is in there I may be missing in my rice burner.

I often roll my eyes when I hear a service writer say on the phone to a client or even worse, to me, ah probably just a gas cap.

How the F would he know? As Kev said,
the parts pushers were fast to recommend a gas cap replacement fix.
Publics dumming down happy to dismiss ANY code as unnecessary emissions BS.

Most ppl don't like having a check engine light on unless they drive jalopies like I do, and just pushing a gas cap is not a pro move, just to have them/client come back a few hrs later really pisses them off. I work on a lot high ends cars lately, I know my clients want me to really check it out thoroughly and not loose their valuable work time sitting in a waiting room cuz the parts counter guy or front desk idiot told them it was a gas cap without even checking it. I laugh so hard sometimes.

Any idiot can plug a code reader. How many times have I seen a counter guy go outside with the hand held code reader/tpms thingy, read code, see evap, run inside, grab a gas cap, run back out, screw that on, erase code, and tell client fixed. Yeah, not a pro move. Then the whole garage looks the fool/tool when client comes back freakin out calling us losers and screaming we are all out for the money grab. Makes me want to choke the front counter guy. Stay where you belong, which is, behind the damn counter. !!:mad:

Anyway, I think this is enough said on this subject for now.
 
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JP

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#7
Actually, there is no way the car can actually know if the gas cap is defective or badly installed. It's just gm's way of saying "hey" I have an evap leak. It will either light a gas cap light or in your case, message center will say to check gas cap and check engine light will come on. Should be tightened to three clicks. Probably is written that on gas cap.

One thing you can do though is check the surface of filler tube where the rubber o-ring of gas cap mates to the filler tube. If you see rust there, clean that off with some emory cloth. Also check the o-ring/gasket for pitting if the tube is in fact rusted. The o-ring can be replaced, but better to replace the cap altogether. They are relatively cheap.

But this does not mean the code will go away if you have a canister problem, stuck evap purge solenoid, or a crack in evap tubing etc.

If no rust is present, and a new gas cap does not help, best bet is to get it checked out with a smoke machine. If the gas cap is still original, the bet on a gas cap fixing the problem is not a monetary conundrum. It is nowadays almost a maintenance item. A gas cap for your car is about 10-20$. That`s the price of a pack of smokes or a 12 pack of beer. But make sure the surface of the filler tube is pristine and smooth. If it is too rusted out, you may have to change the whole filler tube assembly.

I am seeing more and more in maintenance schedules to check or replace gas cap at x intervals in some manufactures.

Here is an example of what I mean. View attachment 10410
Yep. I had two GM cars that had a corroded surface such as pictured. Successfully managed to clean it up and used a new cap, and the code went away. I did occasionally coat the rim of the mating surface with a wee bit of grease to slow down further corrosion. Worked well in both cases, but if the metal is pitted, you might be out of luck and might need a new filler neck.

If you're a "try it and see if it works" guy, try the cap first. If not, as Nick says, you'll need a smoke machine to figure out which part of the evap system is leaking. Lots of DIY youtube videos to make a smoke machine, this one is cheap and looks effective: