CEL- Code 0456 - Question. (Updated-Please advise)
 

Received a CEL Code 0456, "Small EVAP leak detected"

My wife filled up with gas yesterday, and does not recall turning the gas cap until it clicked (she may have, might not have, who can remember, right?) I turned the cap until it clicked a couple times, felt like it might not have been fully tightened, hard to tell.)

Anyway, to clear the code, I just disconnect the negative caple of the battery for 4-5 minutes, right.

I won't be near a computer tommorrow so I will have to fix this in the field.....

If the CEL does not come back on, then it was the gas cap, right?

If it does come back on, it might be a defective gas cap that needs to be replaced, right?

And if, after replacing the gas cap, if the CEL comes back on again, then I need to check all hoses, solenoids, etc, and follow the DTC procedures in the Sticky in the Tech forum, right?

Thanks in advance.

disconnect battery, hold down brake for about 30 seconds, wait 5 or so minutes, then reconnect battery.

Okay, advice and comments please.

I disconnected the battery, held the brake for 30 seconds. Let it sit disconnected. While waiting, I decided to wash the car.

10 minutes into washing the car (with battery disconnected) I realized a window was
%$#@! cracked a quarter inch. So I connected the battery, raised the window, and started the car up to see if the CEL light was gone. Yup, the CEL light was gone. (DSC light was on, not worried about that though)

But the RPM's felt low, like it was going to stall. Gave it some gas to make sure it was back to operating temp. But when I stopped giving it gas, it died.
I figured that the chip just needed to re-adjust once operating.

Finished washing.

Started her up, the RPM's still wanted to dip low and stall, so I figured I'd take her for a run on the highway. Got down the street to the corner, RPM's dropped, the car died.

Started up okay, got it out to the highway, redlined it going north.
But while in 5th gear, cruising at 69, the RPM's were a constant 4,000 RPM.
4K seems high? I dunno, I always thought cruise was <3,500 rpm?

Turned around (I think it wanted to stall at two lights, but I heel/toed it to keep RPM's up) and headed south, and redlined it twice more.

Got home, let off the gas, rpm's dipped to the normal 750 (normal for me in neutral) it did not die. Revved it up several times......it did not die when I let it fall to idle.

And yay, CEL did not come back on.

But I am concerned about it stalling, and the 4K RPM while cruising in 5th.

Did I just need to drive her to let the chip reset? Anything to worry about? Am I just being paranoid?

It is my first CEL, thanks for reading this long diatribe and responding.

this is just a hunch but when you disconnected your battery to clear the CEL you also reset all of your trims.

Give it a couple drive cycles (a couple more times like you drove it today) to see if things stabilize. If it does even out then you know it was just a matter of getting the right trims dialed in... otherwise you've got a real issue to solve.

By "trims"....what exactly do you mean?

Dealer flashes weren't erased, right?

LTFT (Longterm Fuel Trim) is probably the biggest. There are a couple others, shift points, and stuff like that. You may also need to reset your HVAC if you notice your A/C acting flakey.

All of your dealer flashes are still there... it's just the transient data that's been cleared.

So in other words, I may have opened a whole new can of worms by clearing the code in this manner, rather than just letting a mechanic hook up and clear the code?

Are these trims established by the car's chip analyzing driving habits and car performance? Will they re-establish by themselves.......or do I need to take it to the dealer?

It'll stabilize all on it's own, assuming there are no other problems with your car. I used to have to do a "hard reset" every time I flashed a new AccessPort map, which for a while was a couple times a week.

Depending on the tool you use to clear the CEL you may also be clearing the trims anyway.

It's not supposed to be something you need to worry about. Like I said, they'll re-establish all on their own. It's usually not as dramatic as what you describe, more common with FI setups, but I've read of happening with NA cars too.

Just drive a couple more times like you described today and all will be fine. If not, there was some other underlying problem that needs to get fixed, regardless of whether or not you reset your ECU.

Ah, okay. Thanks for the help. I will stop freaking out now.

I'll be patient and wait for things to settle on their own.

Charles R. Hill posted in one of the ECU reset threads I stumbled upon some time ago about an actual procedure you can follow that covers all parameters necessary for the car to re-establish its tuning parameters after an ECU reset.

Idle for 2 fan cycles, 2000 RPM for 3 minutes, 4000 for x minutes, idle again, stuff like that.

The idea is that if you go through all variables and the CEL remains unlit that you solved the problem.