About 2 weeks ago, my SES light came on and NDIS III (and Torque) indicated a P0455 fault. I did the usual tighten-the-gas-cap and reset the code but it returned. Next time I cleaned up the gas cap, filler area, and tightened, but it still returned. This happened when I had less than half a tank of gas and the code returned between 8-10 miles each time. I filled it up the gas, reset the code, and it went 50+ miles before returning.

Today, while driving home, the SES light went off on it's own. I thought once a 'check engine' fault is set, it doesn't go away until you clear it or fix the issue ?

I have bought a new Gates gas cap to try (for $6, made by Gates, in the USA !). I haven't had a chance to inspect anything underneath yet but I'm prepared to buy a canister vent valve solenoid. It's not leaking fuel nor can I smell any so I'm thinking (hoping) the fuel / evap lines are okay.

Why would the light (fault) go off on it's own ?

 

It will be turned off after a certain amount of “driving cycles” without the fault being present.

 

Basically we call a first trip (or a 3 clear start) a "hidden code" because it isn't causing the CEL to turn on. Yes they will self-clear if the issue is no longer present.

 

Basically, if there's a one-time glitch (false positive), it keeps track of it or remembers it for a short period but doesn't throw a code. Only if it does it again within a short period of time, suggesting there really may be something wrong.

FWIW, I ended up changing the solenoid yesterday so I'll see if that was the issue. It's a very simple job, well, except for removing the underbody cover. There's (5) fasteners and two push-clips. I sheared 3 of the 5 fasteners because of rust build-up ! Spent more time trying to remove those and subsequently zip-tying the cover back in place than I spent swapping the solenoid.... It doesn't use the "C" shaped clips that you slide over a metal bracing and creates a 'threaded' hole either. The (3) that sheared look like they may have a welded nut on the top-side of the braces and I sheared off the bolt. If it's welded, my plan of putting the "C" clip in the same location and using new fasteners won't work.

 

Yes, I twisted a couple of those off also, and now have used anti-seize on ALL under body bolt and screws.

 

How did you remove the (welded-in ??) nut ? There's no room to get in there with a wrench (open-end) or vise grips, at least not on the rear two.

If I get them removed, and I've never used anything like JB Weld, could I use that to hold a new nut (stainless steel) for a new bolt (also SS) ?

 

Sorry just saw this, the ones that twisted off, I could not do anything about them, out of all the little bolts and screws that hold the under tray on I am a couple of short right under the motor, fortunately, I have enough holding it up so it doesn't sag.

 

My front undercover has a few that sheared off but at least up there, it uses the C-clips so I bought replacement clips and fasteners and 'fixed' most of them. No sag here either. They certainly put a LOT of fasteners in, more than most people would think are needed.