2019 F-150/Expedition/Navigator vehicles equipped with four-wheel drive (4WD) have a revised transfer case control module (TCCM) strategy that will affect integrated wheel end (IWE) operation after initial start up. The TCCM will not energize the solenoid to supply vacuum to the IWEs after the initial key cycle and a driven gear is selected. The IWEs will remain engaged for 0.8 km (0.5 mi) when the temperature is above 0Ã âC (32Ã âF) and 3 km (2 mi) when below 0Ã âC (32Ã âF). The strategy changes were implemented to improve vacuum supply management and axle warm up in cold temperatures. The engine must run for a minimum of 5 minutes to build sufficient vacuum before performing any vacuum related testing. Refer to the Workshop Manual (WSM) Section, 307-08A - Four-Wheel Drive Systems - System Operation and Component Description for additional information.