Scanner won't scan engine.

Car: 1998 Suburu Forester

My engine light turned on. I went to my mechanic and they claim the connector on my car did not have power. They got power to the connector and claim there was not enough ground to the connector, however, they say the scanner still doesn't scan the car. I am supposed to bring the car back on Friday when I can give them more time. The engine light continues on. The car runs fine. I believe they said their scanner is from Snap-On-Tools. Is their compatibility issue here? What do you think the problem could be?

Thanks, I don't want them to mess up the computer if that is possible. :Cry: