Tried to get my 98 Tahoe daily driver emissions inspected today and it has an "Evap System" code. Does anybody happen to know what usually causes this code or if there is a GM trouble shooting chart on line for these codes? Sorry to post on this site but thought somebody might have run into this.

Sometimes it will set that code if the gas cap wasnt tightened enough.

Is the light on?
If not maybe you can unhook the Groung to the Battery for 10 seconds
and get rid of the code in the putr... then if the light dont come on again, see if it will pass again?
Hopefully others will chime in with more help.

On OBD II vehicles, taking the batt cable off might not clear the code and if it does, you'll have to drive it for about a week before resubmitting it for the emissions test to allow the drive cycles and tests the computer runs to be completed. Take it to a reputable shop and have the truck scanned. It is possible it is a gas cap leak code.

thanks guys, I smelled gas the other day after I turned the truck off and got out so I looked at fuel lines and connections today but I don't see anything obvious. Again thanks for the input, will double check gas cap.

You can get a code reader for about $43 (Actron CP9125 PocketScan at Amazon) that will read codes and reset them. That is likely less than a mechanic would charge to do it so the tool will pay for itself with one use.

I agree that your code is due to a loose gas cap.

Tom

gas cap is most common, see it A LOT