"Check engine" and "service engine soon" are the same thing. The technical term is Malfunction Indicator Lamp, but the vehicle manufacturer can call it almost whatever they want.
If it'* a powertrain code, any OBD-II reader will read it. As mentioned, you'll need something more powerful to read some transmission codes; and all ABS, body/chassis, and other codes.
If you really need the official GM Tech II, best bet is to find a dealership. Those (and the yearly updates) can cost several thousand dollars and are out of the reach of most people and repair shops.
2007 Pontiac G5
1999 Pontiac Grand Prix GT - Stock engine ate transmission.
1997 Pontiac Bonneville SE - Cammed engine ate transmission.