Why does my Silverado keep fixing itself?

tonybolton · Oct 8, 2015

2008 Silverado 5.3 2wd 100k miles

So it will randomly through these tighten gas cap and P codes that are something related to the emissions it drives just fine but the check engine light comes on. I have pulled the code and just kept driving it there's no issues with it.

So I've noticed that after I tow my rig with it once I park the trailer and drop it ...turn the ignition off to unhook everything and then go back to driving it the check engine light stays off for a week or so.

What's up with it?

d_daffron · Oct 8, 2015

Gas cap codes are set by the EVAP emissions system. The tank on your truck is sealed and the ecm pulls a vacuum on it to check for leaks. As for why it does it, the ecm only runs the test when the tank is below a certain fuel level it used to be a that it would only check for leaks when fuel level was below 1/4 tank.

EVAP leaks are a pain to locate. Theres a test port underhood on the fuel tank vent line that leads to the intake manifold. The dealership has a smoke machine that connects to that test port and injects smoke to find the leak.

The problem could be anything from a leaking EVAP purge solenoid, a leaking EVAP vent solenoid, a small hole in one of the fuel tank vent lines, or even a bad gas cap.

EVAP codes will not affect how the truck runs or operates, its just annoying having the check engine light on. Do you usually fill the tank right before you drop the trailer and drive it for a week? That would explain why the light goes off and stays off for a while until the fuel level drops enough to allow the ECM to check for leaks.

muddinmetal · Oct 8, 2015

d_daffron said:
The problem could be anything from a leaking EVAP vent solenoid or even a bad gas cap.

EVAP codes will not affect how the truck runs or operates, its just annoying having the check engine light on.

This ^^^

TBItoy · Oct 8, 2015

If it's too annoying, buy a $125 vin key for EFILive and I'll delete all the EVAP codes for you.

tonybolton · Oct 8, 2015

Re:

Interesting..... Thanks. I'll be in monitoring mode with the fuel level this week.

44BRAND · Oct 8, 2015

Most likely a bad Evap. vent solenoid. That is the most common evap. failure on GM trucks, SUVs. Not hard to replace or real expensive.

tonybolton · Oct 8, 2015

Re:

Yeah Ive YouTubed the evap thing and it doesn't look that bad but honestly it's hard for me to get motivated when it keeps fixing itself.

tonybolton · Oct 9, 2015

Its back on now....

offroadr1 · Oct 9, 2015

Its not fixing itself. The computer looks for 40 keys cycles of not seeing the problem then shuts the light off. Are you female? I hear a lot of female logic

muddinmetal · Oct 9, 2015

That f'n light wont hurt anything... either fix it or quit bitching about it :fish:

pholmann · Oct 9, 2015

Take your gas cap off, flip the rubber gasket and put it back on. If the leak is the gas cap it'll fix it for a while. Holler at me Tony, I can hook up my solus to it and see.

tonybolton · Oct 9, 2015

Re:

I know its not "fixing itself"....

I know how to fix this and I know what the code is I've just never had a vehicle that the check engine light would just randomly shut off like it's doing. I figured once the light triggered it would stay on until the problem was fixed.

For **** sake maybe some of you guys should go bitch at that guy in the red truck for running over the 4 Wheeler some more

tonybolton · Oct 9, 2015

Re: Re: Why does my Silverado keep fixing itself?

offroadr1 said:
Its not fixing itself. The computer looks for 40 keys cycles of not seeing the problem then shuts the light off. Are you female? I hear a lot of female logic

Sorry I thought it look for 52 or 54 cycles of the key I'm sorry I'll go back to school and get my degree on check engine lights.

poolman · Oct 9, 2015

Re: Re: Why does my Silverado keep fixing itself?

tonybolton said:
Sorry I thought it look for 52 or 54 cycles of the key I'm sorry I'll go back to school and get my degree on check engine lights.

muddinmetal · Oct 9, 2015

Re:

tonybolton said:
For **** sake maybe some of you guys should go bitch at that guy in the red truck for running over the 4 Wheeler some more

David 4x4 / Dynamite Design is back. Ol' asshole truggy guy may just luck out now that someone else is here to :fish:

wimpykid · Oct 9, 2015

It's a Chevy molaugh

pholmann · Oct 9, 2015

wimpykid said:
It's a Chevy

Troof

grcthird · Oct 9, 2015

What are the code numbers?

tonybolton · Oct 9, 2015

Re:

P0449 I believe it was....I've got the Torque App and reader. Its been a while since I used it though. Its the valve located under the truck near the gas tank.

Its been a different code a few times but it was the same evap stuff.