When upgrading to a Sync 4 from a Sync 3, some people may have the programming tool FORScan. If they try to connect with FORScan, they may not be able to connect, or see the APIM as a possible directory.
To fix this, the vehicle needs to be in the On position, but NOT engine running. Unplugging the security gateway for about 10 seconds, and plugging it back it fixes this issue. The Security Gateway connector is the plug to the back of the OBDII port.