Four-wheel drive not engaging

SEAGULLOPERATED

MEMBER
2004 FORD EXPEDITION
5.6L
V8
4WD
AUTOMATIC
100,000 MILES

The vehicle listed above is used as a farm vehicle, never on the road. I got the car for free, and it needed brakes and brake lines. I blocked off the rear brakes at the master cylinder and bypassed the ABS module for the front brakes. I just ran lines directly from the master cylinder to each front wheel. I actually ripped out and removed the ABS pump. The 4x4 will not engage. I didn't try it before removing the ABS components so I'm not sure if it worked when I got the vehicle or not. My question is, does the ABS system need to be intact for it to engage 4x4? When I try and switch from 2H to 4H I get the 4x4 light blinking a few times on the dash then goes out. It will not switch into 4x4.

Sunday, March 6th, 2022 AT 10:56 AM

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

The ABS is not part of the 4WD system so that is not going to cause this issue.

This system is pretty simple at this point, so we need to find out what the voltage is going to and returning from the switch.

So, you should have 12 volts going to the switch on the dark blue wire and then a reduced voltage returning on the same color wire depending on which setting you have selected.

Here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-check-wiring

If this appears correct, then the likely cause is the four-wheel drive module.

However, we need to check the voltage from the DTCM to the transfer case assembly.

Please see the wiring diagram below and we can go from there.

Let me know what questions you have. Thanks

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