2019-2020 F-150 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 0 deg C (32 deg F) and 3 km (2 mi) when below 0 deg C (32 deg F). 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.
