Circuit Description: Notes
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
The Vehicle Communication Unit (VCU) and the Vehicle Interface Unit (VIU) communicate using the OnStar® Serial Data (-) circuit, OnStar® Serial Data (+) circuit and the OnStar® Serial Data Return circuit. DTC U1500 is set when the VIU detects no communication between the VIU and the VCU.