I found the TSB below in another post (which I cannot find again?). Does anyone by chance have the "updated procedure outlined in 2006 Workshop Manual (WSM) on-line version, Section 308-07A, Pin Point Tests B21 and B22?" I'm also hoping the vacuum line connection at the wheels is obvious?

I suggested this fix as a preventative measure, but he tells me he is having symptoms exactly like those described. I want to be sure and evacuate any water he may have in the system if, in fact, any is found.

Thank you.

Andy

TSB TEXT:
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FORD: 2004-2006 F-150
LINCOLN : 2006 Mark LT


ISSUE:
Some 2004-2006 F-150 and 2006 Mark LT 4X4 vehicles built before 4/24/2006 may exhibit a noise in 2 wheel drive from the front Integrated Wheel Ends (IWE) and/or the 4X4 system being inoperative. The IWE solenoid may have ingested water and passed it to the IWE system causing water contamination in the vacuum portion of the system. A shorted IWE solenoid can set the codes C1979 and C1980. If either code is present, the 4WDH light will be inoperative.

ACTION:
Use the following Service Procedure to check and repair the 4X4 system.

SERVICE PROCEDURE

Replace the IWE solenoid. Torque the new design bracket and solenoid to 62 lb-in (7 N-m). It will be necessary to remove the vacuum lines from each IWE down at the wheels to check for water being present.
If no water is present at the vacuum line at the IWE, install the new solenoid with bracket. Reconnect all vacuum hoses.
If water is present allow it to drain from the vacuum lines. Then follow the updated procedure outlined in 2006 Workshop Manual (WSM) on-line version, Section 308-07A, Pin Point Tests B21 and B22. These tests checks IWE leak rates with vacuum and will remove any residual water from the IWE. Reconnect all vacuum hoses.
If the IWE looses vacuum quicker than specification. Refer to WSM, Section 204-01B for normal diagnostic procedures.

PART NUMBER PART NAME
6L3Z-9E441-A (CX-2117) IWE Solenoid