Test G: the Front Axle Makes Noise In 2H Mode Only and Generally Under Heavy Throttle

Pinpoint Test G: The Front Axle Makes Noise in 2H Mode Only and Generally Under Heavy Throttle

Refer to Vehicle/Diagrams, Four-Wheel Drive Systems for schematic and connector information.

Normal Operation

In 2H mode, the 4X4 module provides a ground path to the Integrated Wheel End (IWE) solenoid to supply vacuum to each IWE (disengaging the front hubs from the front axle). During certain conditions such as wide open throttle (WOT) maneuvers, manifold vacuum is lower than desired. To maintain uniterrupted IWE function in 2H, stored engine vacuum is sourced from the vacuum reservoir. A primary 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. There is a secondary one-way check valve (adjacent to the IWE solenoid) which protects the IWE from a loss of vacuum in the event that the vacuum reservoir has a leak and manifold vacuum is low. For noise-free IWE operation under all conditions, both check valves must be operating correctly.

This pinpoint test is intended to diagnose the following:

^ Vacuum leaks
^ Vacuum check valves
^ Vacuum reservoir
^ IWE solenoid
^ IWE

G1-G4:

G5-G8:

G9-G12:

G13-G16: