gm tech question, sorry...

[xwaynestaticx03]

im working on a weird issue at work and wanted to pick the brains of any tech that might be on the site... i have an 01 pont grand am 2.4 L im trying to cure a check engine light issue on. its throwing an evap code 0440. i believed the vent solenoid to be bad, but the code returned after i replaced it. normally this would end up being something silly like a loose gas cap or a stuck vent solenoid. when i smoke test the system, the vent solenoid checks out fine. i am not finding any other leaks, but i did find that i have a blockage in the system. i do not see any smoke at all with the cap off or even with the filler neck disconnected. have any of you guys run into this before? im thinking either the line from the charcoal canister to the sending unit is clogged or could the canister itself be bad? sorry for the long post and the gm question, just trying to get this fixed right so the customer isnt pissed at me anymore...

 

[rmchrgr]

First off, do you have a diagnostic tree for the code and a wiring diagram from GM or All Data or something? That would help.

The smoke machine doesn't always show leaks, especially very small ones. Check for cracks with your eyes and hands. I fixed a P0456 code by feeling a hose with my fingers that I couldn't see. I think your code is a system code and not a leak though.

Can you test the system with a scanner to see if it will give you info?

Is it Pulse Width Modulated? Can you find the slot on the PCM and check it with a scope or voltmeter to see if the PCM is seeing the right info? Verify your voltage first, then trace the circuit back to find the issue. Bet it's NOT the PCM. Probably a bad wire somewhere.

That's what I'd do before replacing parts. Need to verify what you have first.

Hope that helps. Evap codes SUCK. Good luck.

 

[xwaynestaticx03]

yeah, its not a leak code, is a system malfunction... i wish it was a leak, it would be fixed easy. ive got mitchell at work, but i dont trust it alot of the time. after giving it some thought, im fairly sure the fault is in the charcoal canister or the line going from the canister to the sending unit. if i close the vent solenoid and disconnect the filler neck i get nothing smoke wise from the tank. that leads me to believe somethings clogged or closed thats not supposed to be inbetween the tank and the rest of the system. the cars coming back sat. morning for me to mess with so ill let you know how she goes... thanks