Circuit/System Verification
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
If there are any other engine or transmission related DTCs set, diagnose those DTCs first. With a scan tool observe the PNP Switch parameter in Engine Data list and move the gear shift lever from Park, to Reverse and through all the Drive ranges and observe the parameter as you move the shift lever. The parameter should display Park/Neutral when in Park or Neutral and In-Gear when in Reverse, Drive or Drive Low ranges. It is especially important to closely observe the Park and Neutral to Drive transitional positions while moving the shift lever and observing for possible misalignment or slack in the shifter mechanism. Refer to Transmission Internal Mode Switch Logic .