Does the rest of your gauges work properly? Were you able to find an OBDII plug in the driver's compartment under the dash? If so, then I don't know why it can't read your car?
I remember when you first plug the SGII in, it takes a few minutes to "read" your car and then is ready for use. Try unplugging it and plugging it back in and wait a few minutes; then check the code reader.
Let us know how it works out Mensajero.