[wiswind]

You will find that there are a number of choices.
1 group are those that will connect to your laptop computer.
These will offer you the most in features, however, they require you to use your laptop computer.
With these, you can read real time trim information, and graph results, etc.

The next group are the stand alone units that do not require a computer.
They will be more limited in features.
I have a "ScanGauge" that I keep connected to the OBDII port all the time.
When a failure code is set, it will do a freeze frame collection of data that was present at the time the code was set.
This unit has far less features than the ones that connect to your laptop, but again, has far fewer features.

I would strongly recommed that you get one that can read the "CAN" codes as many newer vehicles use that coding method, and you will be able to use it on more (newer) cars.