Check Pin #16 on the Data Link Connector (DLC) for battery voltage. (See Diagram)
If there is no battery voltage present check the fuse marked "OBD II" in the engine compartment fuse block. It is a 10 Amp fuse. If the fuse is good, repair the circuit between the fuse and pin #16 at the DLC.
If battery voltage is present at Pin 16 at the DLC, check for ground at pin 4 on the DLC. If ground is not present, repair the ground circuit between the DLC and Ground G202 located at the left side of the dash.HINT:
the easiest way to check BOTH of these at the same time is to use paper clips plugged into pin #16 and Pin #4 and connect a light bulb between the two. If the light illuminates brightly, power and ground are both OK.
If no problem with power or ground is detected at the DLC, check the Owner's Manual for your code reader.