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Old 09-26-2010, 04:14 PM   #1
kmacht
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Default Chevy Cavalier Evap System Problem

My brother in laws car (a 2003 chevy cavalier) was throwing two error codes causing the check light to come on. Seeing how he doesn't have alot of spare cash I agreed to take a look at it for him. The first code was easy. It turned out to be an oxygen sensor. We replaced that, reset the computer, and that cleared the code. The second code he was getting was P0442. This is a slight evap leak detected. I had him go to the auto store and buy a new gas cap, reset the computer again and see if that does it. It didn't. So I am looking at some advise on what to check next. All the cars I have ever had this type of code come up on have cleared themselves with a new cap. What else could be leaking, where would it be, and how do I check? I know that the professionals use a smoke machine to find leaks. I just want to do a visual inspection of the likely parts to see if there is anything obvious (cuts, tears, etc). The problem is that I know little about the evap system, how it works, or where the componenets are located. Any help or advise you can offer is appreciated.

Thanks,

Keith
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Old 09-26-2010, 04:49 PM   #2
ozzy214
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Default Re: Chevy Cavalier Evap System Problem

You are mistaken. Evap small leak is almost usually never a cap. Only evap large leak is normally the cap. Only way is to smoke the lines and watch for the smoke. Follow the under hood diagram for the evap lines. They will run from a vacuum source to the carbon canister all the way to the tank.

other way is maybe pressurize with air and leak test with some soapy water. About all ya can do from home. Evap small leak is mostly a loose line or split hose, but I have seen the fuel tank sending unit gasket cause the code as well.
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Old 09-26-2010, 05:17 PM   #3
Moltar
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Default Re: Chevy Cavalier Evap System Problem

Evap vent control valves commonly fail since they're almost always open and only close for system tests. So when the ECM performs the leak test during a drive cycle the vent control valve is so used to being open it gets stuck.
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Old 09-26-2010, 05:32 PM   #4
srmofo
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Default Re: Chevy Cavalier Evap System Problem

I hate evap codes. Its not they are hard to diagnose, but sometimes they can take hours to find.

In my experience with that vehicle I have noticed that the canister vent solenoid has a pretty high failure rate, followed by the purge solenoid. The fuel tank sending unit gasket has come up a few times also.

Unfortunately its going to be tough to diagnose it without a scan tool or smoke machine. You can visual inspect all the lines and activate the solenoids with some jumper wires to make sure they are even functioning, but that will not tell you if they are holding vacuum or pressure.

My advice is to live with the light until he can take it to a reputable shop and get it right the first time. theres no sense in throwing parts at it considering it can be anything in that system from a small o-ring to the FTPsensor
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Old 09-26-2010, 10:04 PM   #5
pp702nw
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Default Re: Chevy Cavalier Evap System Problem

My GF had a po442 code in her 04 cav. The problem seem to be from her packing the tank full of fuel. After correcting her on not packing fuel in the tank, the po442 code only came up intermittently and disappeared after a couple of weeks and never returned.
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Old 09-26-2010, 11:01 PM   #6
Lotek
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Default Re: Chevy Cavalier Evap System Problem

Quote:
Originally Posted by ozzy214 View Post
You are mistaken. Evap small leak is almost usually never a cap. Only evap large leak is normally the cap. Only way is to smoke the lines and watch for the smoke. Follow the under hood diagram for the evap lines. They will run from a vacuum source to the carbon canister all the way to the tank.

other way is maybe pressurize with air and leak test with some soapy water. About all ya can do from home. Evap small leak is mostly a loose line or split hose, but I have seen the fuel tank sending unit gasket cause the code as well.
Bad idea, evaporative emissions systems operate under pressures measured in inches of water, less than 1 psi. Pressurization with shop air, even regulated as low as you can go has a good chance of causing damage or an explosion
I have seen fuel tanks on cavaliers crack at the filler inlet, sender seals that weren't installed correctly, (has the fuel pump been replaced?) and bad vent valves. May be worth paying an hour to have someone smoke test it, if you don't have the tools, you would need a smoke generator and a scantool capable of activating the vent and purge valves.
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Old 09-27-2010, 08:41 AM   #7
SpiderGearsMan
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Default Re: Chevy Cavalier Evap System Problem

p0442 ? check the evap vent solenoid hanging open or the canister purge solenoid
also , on n cars , the sender gasket used to leak
the trick is to seal the system , I use a tech 2 , but the otc genesys will work too , and use a smoke machine
not really backyard mechanics tools
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Old 09-27-2010, 08:49 AM   #8
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Default Re: Chevy Cavalier Evap System Problem

This is why I drive an '85.
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