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Originally posted by 06ragtopgt_SOS:
I'm not sure exactly how its set up on your particular car. But land rover (what I work on) uses a DMTL (diagnostic module- tank leakage) pump to check for evaporative emission leaks. A fine leak is .5 to 1 mm. Anything over 1mm is a gross leak. It checks these by measuring the current it takes to push air through sample orifices built into the pump and then comparing it to how much output there is in the rest of the system. Start with the obvious, like a gas cap as mentioned above. But if that doesn't do it you might have the system smoke checked. They plug a smoke producing machine into a test port and smoke will leak wherever your issue is at. For example, a common one for us is stuck open purge valves, and often the DMTL pump itself is just shot. Hope this provides a little insight into what you're up against.

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