Why Won't the Horn Work on a 2001 Ford Expedition?by Richard Rowe
A perfect machine would perform an endless number of tasks an infinite number of times, using exactly zero moving parts. The horn circuit used to be one of the simplest parts of any vehicle's electrical system with little to go wrong and little to fix if something did go wrong. But time marches on, things get more complicated, and horn systems like those used on the Expedition contain at least a dozen possible failure points in the horn mechanism and the adjutant electronics.
This should be the first thing you check, since a blown fuse can both cause a horn malfunction, and indicate bigger problems. You can find the horn fuse -- a 20-amp unit -- in the battery junction box under your hood. Specifically, in slot number seven. This fuse is actually the one that provides power to your anti-theft module; the horn works through the module and gets its grounding signal from the module. If the fuse is blown, not only will the horn not work, but you should get several codes from the diagnostic computer indicating an anti-theft system malfunction. You may also try replacing the horn relay; you can find it in the fuse box and identified by a diagram printed on the box lid.
You can find the horn mechanism itself behind your front bumper, just to the right of the radiator core support. This is the part of your system that actually makes sound and it requires nothing more than power input to do so. The simplest way to test the horn mechanism is to unplug it and probe the chassis-side terminals of the connector with a test light. Have an assistant hit the horn button. If the light comes on, then you have a bad horn mechanism. If it doesn't come on, then the horn mechanism likely works, but isn't getting a grounding signal from the anti-theft module.
If you're not getting power to the horn, and all your anti-theft systems are working, then odds are good that you have a problem with the horn switch in your steering wheel. The horn button is easy enough to access and test; you need only remove the two bolts on the back of the steering wheel to release the airbag module. But therein lay the problem: the horn switch is integral to the airbag module, and that is not something you want to mess with. Can you deactivate it? Yes. But anyone who's willing to hand a DIY mechanic written instructions on disabling airbags doesn't care about whether or not he kills himself in the process. We do. So, this is where you take your truck to a professionalmechanic and let him risk his neck with a potential airbag detonation.
Because of a change in wiring length in the horn system, some 2001 Expeditions are known to have problems with a weak chirp when using the key fob, or no operation with the engine off. Ford issued a technical service bulletin in 2002 describing this issue, so any dealership will know about it beforehand. You can fix this at home, but don't even touch your truck's wiring unless you know exactly what you're doing. In this case, you're far better off getting ripped by dealership mechanics than risking damage to the truck's electrical system. Or risking an airbag going off in your face and turning you into a full-scale Pez dispenser.