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Pinpoint Test O : The Front Axle Makes Noise In 2H Mode Only And Generally Under Heavy Throttle: Notes

WARNING: This page is about a different car, the 2018 Lincoln Navigator. However, it is still accessible from the selected car via links, so may be relevant.

Refer to Wiring Diagram Four Wheel Drive Systems for schematic and connector information.

GFD274030Courtesy of FORD MOTOR COMPANY
Item Part Number Description
1 - Vacuum input line
2 - Vacuum check valve
3 - Vacuum reservoir tank
4 - IWE solenoid
5 - Vacuum output line

Normal Operation 

In 2H mode, the TCCM provides a ground path to the IWE solenoid to supply vacuum to each IWE (disengaging the front hubs from the front axle). During certain conditions such as WOT maneuvers, manifold vacuum is lower than desired. To maintain uninterrupted IWE function in 2H mode, stored engine vacuum is sourced from the vacuum reservoir. A one-way check valve is implemented between the manifold and IWE solenoid/vacuum reservoir to prevent the stored vacuum from escaping into the manifold during low engine vacuum conditions. For noise-free IWE operation under all conditions, the check valve must be operating correctly

NOTE: When shifting to 2H mode in order for the IWEs to completely disengage the vehicle steering wheel must be less than 90 deg and 5 seconds have elapsed since the shift to 2H has been initiated.
NOTE: The TCCM has a cold strategy which is used to warm up the front axle in cold temperatures to improve driveline synchronization. When ambient temperature is below 32 F (0 C), the IWEs engage after the initial key cycle and a driven gear is selected. The hubs stay engaged regardless of 4x4 mode change for approximately 2 miles (3km). Once distance traveled has been achieved IWEs disengage if vehicle is in 2H. Distance traveled resets only if the temperature is below calibrated threshold and another key cycle has occurred or customer shifted to park and back to a driven gear within the same key cycle.

Possible Sources 

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