Conditions for Setting the DTC: P0851
WARNING: This page is about a different car, the 2009 GMC Yukon and 2009 Chevrolet Tahoe. 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.