Conditions for Setting the DTC: P0851
WARNING: This page is about a different car, the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The ECM detects the Park/Neutral switch signal equals 12 volts, high, when the IMS reports a Park/Neutral range for 3 seconds.