2006 Chevy Silverado OBD II wont read codes

The check engine light came on 2 days ago, so I hooked up the obd hand scanner and linked it. Came back with zero codes. Why would it do this, talked to a few mechanics shops and they said it could be a dealer specific code, but like I told them my scanner has a good amound of chevy codes, thats why I got it. But they were clueless which leaves me clueless. Any help would be nice!