I'm looking for the steps to find and/or re-program the code used with the keyless entry system. In other words, I don't know the code for my vehicle's keyless entry system. What should I do?
Ford's factory 5-button keypad systems have a factory code, which is always active, and also can be programmed with a personal code.
The factory code is on the "owner's wallet card" and is also printed on the computer module. In the '01-02 Expedition, the computer module is buried up in the dash behind the radio, though people claim you can read it with a mirror and a flashlight.
Once you've got the factory code, you can program a personal code using the instructions in the owner's manual, e.g.: [PDF] http://www.motorcraftservice.com/pubs/content/~WO5HDW/~MUS~LEN/41/05hdwog3e.pdf#page=91
Please also note that the entry code
GEM - Generic Electronics Module
RAP - Remote AntiTheft Personality SJB - Smart Junction Box
Early 90's fords, anti-theft and Keyless entry was a feature. The RAP was created to augment a vehicle model with existing electric locks. This is kind of like what aftermarket Keyless entry / Alarms modules were. You won't find RAPs in them much more. This lead the way to GEM's.
A GEM is like an engine management computer for all the non-power-train systems in the car. It does communicate with the power-train system. A GEM controls the Lights (autolamps), wipers, rear window/mirror defrosters. It control the Locks, and the keyless systems too now. This module is what would need to be-replaced if you wished to change the Keyless entry code. This has also been replaced in later-models with the SJB.
The SJB is marriage of the GEM with the internal Fuse panel in to one, inseparable unit. As, always there are exceptions.
As an alternative. If you merely wish to disable the keypad, that is also a possibility. These, use a combination of 8 - 6 wires to send the key presses to the GEM/RAP. An inclined DIYer can examine the wiring charts available on AutoZone's Member site. This would involve cutting of one or two wires to disable the keypad.
If you want to find the code but cannot find any documentation of it, if you take it to your local Ford dealer they can hook up their computer to it to let you know what the code is. Unfortunatly it has to be the Ford computer system so even if you have an after market one it will not work.