Computer problem
2000 GMC Jimmy 6 cyl Four Wheel Drive Automatic 90k miles
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Took car in for mechanical and emmisions inspections. Passed mechanical but could not get readings for the emmisions portion. I took my car to parts store and borrowed their scanner and got the same results. What troubleshooting step do I need to take to fix this problem?

Did you check the lighter socket fuse? They usually power the OBD connector as well. If it blows the testers won't be able to communicate with the ECM.