Conditions for Setting the DTC
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
DTC P0873 sets during steady state operation when E solenoid is commanded ON and E pressure switch fails to switch ON after 0.1 second of E solenoid being commanded ON.