A couple questions.

[Clark73]

1996 Rodeo 3.2L 4x4

Since the day I bought my rodeo the check engine light has been on. (I got screwed by the dealership) Just recently I've been trying to fix the problems and get the light to turn off. About a couple months ago I took it into autozone to get their free test. The guy who plugged it in started it and told me there were about 30 codes on the computer. Most of them were 02 sensor related and said that new sensors would clean up most of the codes. Well I just went in agian a couple days ago to buy some injector cleaner and I started talking to a different guy and just for the hell of it we plugged it in again. This time though he didn't actually start the car. He just turned it to the on position. He said that there were only 2 codes this time and that my 02 sensors were fine. I hadn't replaced them yet either. My question is does the car running affect the codes the computer puts out rather than it just being in the on position? And if it doesn't, how is it possible for almost 30 codes to just dissapear?

My next question is that one of the codes says that my fuel system doesn't have the pressure it should. I know this code is correct because I don't hear a hiss when I open the gas cap. I replaced the gas cap hoping that it would be a simple fix but no luck. Is this most likely a leak somewhere or something else. If it's a leak I was thinking it would maybe be in the hose to the evap canister or even the evap canister itself. Does anyone know where this problem would most likely be coming from? Any help would be greatly appreciated. Thanx.

[highlandlake]

"how is it possible for almost 30 codes to just dissapear?"
Perhaps the autozone person cleared the code history - it's easy and normal to do that.
Can you post the current code numbers here and see if some specific advice will result?

[Clark73]

I went into autozone again today and the code was P0440. He told me that it has to do with the gas cap so we erased the code since I already replaced that. So hopefully the CEL will stay off now.

Also I was told that it shouldn't make a diff if the car is running or not. But doesn't your car HAVE to be running when it's plugged in for a smog check?

[lifelongslacker]

I have the same prob with that code. On mine I can see a small hole in the tube that you use to fill the tank. (near the gas cap side)
You can clear the code, but it will probally reappear in a few weeks.
As long as you are not leaking gas, it isn't that big of a deal.