I have a 2001 Excursion 4X4 limited with 127,000 on it. My 4X4 dash light comes on but the system does not engauge. I have heard this is a common problem and it is usually the front axle actuator plunger not working. I am looking for a repair procedure to verify the issue and fix it. Can anyone help? Thanks.

 

Engage the hubs by hand, turn them to "LOCK". Then try 4x4 and see if you have power at all four wheels (nailing the gas in the dirt should do the trick).

If so, your hubs are not locking. It sounds like it, because the light is on on the dash. The light only comes on when the switch on the transfer case says it's shifted fully into 4x4, so the only thing left is the hubs.

First, check all the vacuum hoses from the knuckles back to the vacuum solenoid on the passenger-side fender. A 2001 should be having vacuum hose "issues" at this point Usually right at the knuckle.

Now, find the hose from the vacuum solenoid to the vacuum canister/reservoir, and make sure you have vacuum at the solenoid. Then, find the hose from the vacuum solenoid going towards the hubs. Disconnect it somewhere convenient, and put a vacuum gauge on it. While watching the vacuum gauge, turn the **** from 4x2 to 4x4. You should see vacuum for about 40 seconds, give or take. Then turn it back, you should see it for something like 10-20 seconds. The unlock vacuum pulse is shorter than the lock pulse by about half, I forget the exact numbers. You can always do it by the stick-your-finger-on-the-end-of-the-hose method too

If you don't see vacuum at all right after the solenoid, it probably means the vacuum solenoid is bad.