Once in a while we run across a vehicle that has no power to the OBD2 port, which means our module cannot power up. This is usually due to the OBD2 fuse being blown and in most GM products this is shared with the CIG LTR fuse (not to be confused with the AUX PWR fuse, which is the other sockets).
This fuse is usually located under the hood in the fuse box and labeled as CIG, CIG/LTR or CIG/OBD. An example of a typical Silverado fuse box is shown above.
Your OWNERS MANUAL should have a diagram of your fuse box layout and the fuse positions/labels in the MAINTENANCE section. The OBD related fuse is normally located in the "in-cab" fusebox under the driver's side knee bolster OR in the side of the dashboard as you open the driver's side door.