Scan Tool Does Not Communicate With Class 2 Device: Description
WARNING: This page is about a different car, the 1999 GMC Sierra and 1999 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Each module on the Class 2 serial data link which is powered and performing functions that require detection of communications malfunction is required to send a Node Alive message every 2 seconds.