If you have the owner's manual for your Explorer, it may still have the little credit card sized card with the keyless code printed on it. If no card, then maybe a previous owner wrote the code in the manual. Check inside the front and rear covers, if not there, then open to the section on the remote keyless entry and see if it's written on those pages. Those pages will also explain how to program a personalized code once you know the factory code.

If none of that works, you may need to find someone with a professional scan tool who can access the module and read out the factory code.

-Rod