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I have a 2003 GMC Sonoma that popped the p0442 "Small Evap Leak Detected" code.

I replaced some vacuum lines in the engine compartment, replaced the purge solenoid and still got the code. So then I start to look at the vent solenoid. I inspected the hard plastic vacuum lines from the solenoid to the canister over to the fuel pump (from what I could see without lifting the bed) and those seem in good shape. Removed the vent solenoid, no cracks, bench tested it with 12V successfully, and blew air into it while it was closed to verify no leakage. So then I started to look at the connector to the vent solenoid. The wires seem intact, and when I start the truck I get ~14V at the connector unloaded. As soon as I plug in the vent solenoid the voltage drops to about 0.1V and there is no click. The coil impedance is around 22 ohms. I had the old purge solenoid available (coil still worked), plugged that in with the same result, voltage drops, no click. Purge solenoid coil impedance is ~19 ohms so not too far off load wise. I suspected a bad ground, followed the wiring harness to the rear of the truck and cleaned the two ground connections there. One other thing to note, I noticed when I was filling the gas tank the other day I heard a high pitched whistling coming from somewhere between the gas tank and the vent solenoid (couldn't confirm where). I reset the codes again and will drive it to see if it comes back but in the meantime:

Questions:
1) Does the voltage at the connector seem to be behaving correctly?
2) Is the whistling sound just from the vent solenoid when its open and the truck is off?
3) What else should I be checking? I haven't yet committed to doing a smoke test, I don't have a machine and not ready to drop $100 to have it tested at the shop yet.
 

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It's mostly BS
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1. The voltage should stay 12-14v or so since the vent requires constant power. The ECM provides a control ground when closing the vent.
2. The vent is normally open when filling the tank, so it is expected air will pass through it. Not sure why it's whistling.
3. Check the gas cap and rust thru areas on the filler neck.
 

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It's mostly BS
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You'll need a bidirectional scanner to trigger the ground to the vent valve. You're not likely to catch the vent ground signal without a scanner since this only happens during system self test. If there was something wrong with the ECM command and the vent was not being actuated, you'd probably be getting a "large leak" P0455 or one of the circuit fault codes P0443 thru P0449.

Since this is a small leak, a leaky vent, leaky purge, leaky hose, leaky tank, leaky cap, leaky canister, leaky filler neck or any other part of the system can cause this. That's why people like the smoke testers.
 

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Welcome to the forum.

Sounds like coincidence.
Possibly the vent hose from the tank was leaking at the pump and replacing the pump re-sealed it? Or maybe the pump to tank seal was leaking? The other 2 hoses would have leaked fuel. Or I suppose there could have been a pin hole rusted through the top of the pump?
Were you getting a P0442 DTC prior to the pump change?
 

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It could be the o-ring around the fuel pump or the o-ring under the pressure sensor on top the fuel pump dried out and leaking. The pressure sensor o-ring dried out on my 02 Chevy Astro got the same code P0442 replaced the o-ring no more code.
 
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