Code P0455 and the Gas Cap

[guruerror]

Originally Posted by guruerror

Now I'm getting P0455 and P0496 High Purge Flow...blah blah. I guess it's time for the smoke test.

I've also notice on my last three gas-ups that immediately after putting gas in the tank (whether it was a complete fill-up or not) when I turn the key the engine cranks really fast and starts to start, but then putters out (like it's not getting any gas). When I turn the key a second time, it gets a little better and almost idles, then putters out. On the third try it usually starts after a few cranks but idles rough for a bit, then it's fine and doesn't act up again until I put more gas in.

WTF?

I'm thinking maybe the purge valve up front needs replaced...$40 (GM 12581282).

I was poking around on a Cadillac forum where the same code and symptoms were discussed: "The first time it happened was after stopping to refuel after being on the road for about 4 hours. The car wouldn't start, even after letting it sit for a bit. Finally, I pressed the gas peddle all the way down and it fired up (acted like it was flooded)."

The Cadillac tech reported that this was a "condition that we used to refer to as 'flow during non-purge'. Basically the engine is sucking fuel vapors from the canister into the engine which will severely enrich it. If the computer doesn't know this is happening the fuel mixture won't be right and it will not run well."

Replacing the valve seemed to resolve the issue for the Caddy guys...guess I'll give it a try this weekend.

[HUMTECH]

Simple to test, unplug the electrical connector on the purge valve then disconnect evap line from cannister at purge valve with engine running and check for vacume at purge valve connector. If vacume is present valve is stuck open as it is a normally closed valve.

[snmazer]

I apologize for hijacking a thread but I have the same codes and when I start my Hummer I get a extremely loud hissing sound for several seconds then it goes away. If I turn off the heat or AC, the hissing immediately stops. Any idea what this may be? I see you guys are talking about a "purge valve" and was wondering if that may be whats causing my problem?

[guruerror]

Originally Posted by snmazer

I apologize for hijacking a thread but I have the same codes and when I start my Hummer I get a extremely loud hissing sound for several seconds then it goes away. If I turn off the heat or AC, the hissing immediately stops. Any idea what this may be? I see you guys are talking about a "purge valve" and was wondering if that may be whats causing my problem?

I don't have a hiss...just trouble getting started after a gas-up. I've already replaced the 'usual suspects' (gas cap, evap solenoid)...I'm gonna do the purge valve tomorrow and see if that fixes anything.

[HUMTECH]

Im confused as to why you wouldnt test it before replacing parts.

[guruerror]

Originally Posted by HUMTECH

Im confused as to why you wouldnt test it before replacing parts.

That's what I'm doing today. I'm fairly certain that it will react as you described.

[guruerror]

Yep...the valve was stuck open. I slapped the new one on and cleared the codes. We'll see how it goes.