EVAP trouble code, Emissions "Small System Leak"

Tom wrote in news:hbncq5$vv6$ snipped-for-privacy@aioe.org:

That text description is worse than useless, and is even probably wrong.

You need the actual alphanumeric error code that reader saw. It will be in the format of a letter and four numbers, such as "P0457", or "P1456".

Also required is the make, model, year, and engine of the car in question.

Oh come on, just get the crystal ball out...

Personally I wish the "free code reading" crews did it real simple. Pull in, plug in the box, Tell customer - You have a code PXXX Have a nice day...

Then when they ask questions online:

Year: Make: Model: Engine: Trans: CEL on/off Codes pulled: (actual code numbers, NOT what they think it means) Any recent work, additions made: Symptoms:

That at least gives you a starting point.

For instance:

2002, Chevy, Blazer, 4.3, Auto. CEL - OFF Codes present = P0300 - (Random/Multiple Cylinder Misfire Detected so you don't have to look it up)

Owner changed plugs, wires, cap, rotor about 3000 miles ago.

Vehicle seems to run fine, however the CEL flashes while the engine is under heavy load, such as going up-hill or in passing gear.

This gives a starting point. BUT does it also give a solution? NOPE. there are a LOT of things that can cause this code.

Bad cap/rotor, Dirty fuel filter, Dirty injectors, Timing chain stretch Failing coil, Air leak downstream of the MAF, Bad fuel pump. For a start.

That's often true, and also you can spend some time and money chasing codes around a car, and replacing components that were okay, because it's hard to tell what was the real *root* cause. We're not quite at the "Geordie, have the computer run a Level 5 diagnostic on the sensors" stage yet, though a lot of car owners might not understand that -- the on-board diagnostics are just an aid (though a good one) to a skilled mechanic who can bring other knowledge to the table.

As for the original poster's problem, some states have added a gas-cap test to their smog check routine. They don't just look at it; they screw it into a receptacle connected to a vacuum pump and see how well it actually seals. The test seems fairly finicky and dependent on the quality of the O-ring in the gas cap. This might be another way to get some data on the problem, though if it's the standard sort of gas cap rather than some weird proprietary model, it might be worthwhile to ignore my usual advice and just throw a new part at the problem, rather than invest much time and diagnostic expense in lower probability failures.

Cheers,

--Joe

Have the code cleared. Drive it and see if the light comes on again. If it comes on again, have it read and right down the code #.

Could have been the gas cap wasn't on tight enough and set the code. Don't go chasing a code without clearing it and driving it for a length of time to see if it comes on again.

I did specifically ask for a number, but the guy read the text out instead to me in a way that made me think there was no number - I guess that was incorrect. I suppose I have to go back.

That was my original thought, but I'd been told by a repair shop that the modern system will test again and again at interval, and if the problem were to be gone, then the system would clear the code by itself. You're saying that's not true?

Yep, I guess I should have mentioned here: 2002 Buick Century V6, auto

Steve W in a reply mentioned symptoms. When I first encountered this problem a few weeks ago, I thought the brakes were weak. That's when I looked at the dash and saw the 'Check Engine' notice. So the vacuum connection might be there.

The brakes seem okay now. Going on the idea that the problem was temporary (and I've tightened the gas cap several times just to eliminate that, since the first day of the problem), it seems like a good idea to reset the code.

How do I reset the code? I'm reading that disconnecting the battery won't do it, that maybe the scan tool at the auto parts stores will do it. Then there's the usual conflicting info.

Tom wrote in news:hbnv3s$mm9$ snipped-for-privacy@aioe.org:

It's a terrible idea to erase the code without making note of what it was. And the guy who gave you the text-only wasn't too knowledgeable about what he was doing.

Disconnecting the battery will do it, but that will also erase the engine computer's idle-learn and the transmission's shift-learn (or is it properly called "grade logic"?), and probably other stuff as well.

A scan tool is the correct way to erase the code. And if you're going to plug in a scan tool, you might as well record the code before deleting it.

Steve W has posted an excellent summary of the information needed to help discuss and solve these sorts of problems online. You'd do well to read it.