Hello everyone, I'm at my wits end... I've replaced every component of my evap system I can come across, some 2-4 times. 2012 Suburban, 5.3L, 240,000 miles. I've narrowed the issue down to wetness. I know that sounds weird, but my CEL will now only come back on with the P0455 code when I go through a car wash or it's raining and wet. I assume that means an electrical issue? Does anyone know of some electrical connections or grounds (location) that I should check that are common issues? Any help would be greatly appreciated!

 

That's what happens when you fire parts first, instead of diagnosing. So now you need to diagnose properly anyway, after having needlessly spent all that money.

So P0455 means there's a large leak in the EVAP system.
The way the computer detects this, is that it opens the purge valve, and closes the vent valve, to draw a vacuum on the system, and then measures the pressure.

Since you've replaced everything, I'll presume you changed the vent valve, and all the tubing as well, so the plumbing is probably OK. A vent valve that didn't close when requested would cause a large leak, and since you change the valve, the problem must be in the harness. That would also explain why wetness makes it worse.

It's going to help big time to have a DMM, a test light and diagnostic tool because that's the only way to trigger the vent valve so you can test for power on the connector. Use the DMM measure to resistance between ground on the connector (black wire) and bare metal on the frame .... it should be less than an ohm. You're mostly like going to have to inspect your harness for faults and water ingress. The grounding point shouldn't be too far away from the charcoal canister.

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