First of all you really should do your research as to whether this item will work on your model of vehicle. You've got to find that out either online or possibly in vehicle manual. Because there are at least two types of scanner. It works fine on the Hyundai Amica. Probably be great if the manufacturer went into detail (about the vehicles this works on) rather than make people angry and dissappointed. English was probably not the first language of whoever composed the instruction manual ;) but it's still quite easy to follow. I thought I had bought the wrong type, when I tried it, because twice I got a 'linking error'. The manual tells you to turn on the ignition at a certain stage in the proceedings. First turn of key in Hyundai was turning on the stereo, second turn (before actual driveability) was the one the U480 wanted. Where the fans come on... So don't give up on it if at first it doesn't want to talk to the car it's supposed to be able to talk to. There's an extensive list of codes, in the manual, that can help you to decide whether you need to call a mechanic/take it to a dealership immediately or maybe it's something that can be scheduled for sometime within the next couple of months. You do need to check out the codes online, though, because "Main catalyst below threshold" isn't saying anything to me! Find out what the codes are probably referring to and what common issues might trigger that warning light. I would recommend this for the right vehicles.