1998 Ford Explorer XLT 4 WD, Auto, 4.0 litre, V-6 104,000 mil

I visited your site before about the 4wd high + 4wd low lights flashing on my dashboard. I noticed that somebody else had the same problem, and I'd like to ask if there is a device that can check for codes on the powertrain control module, and where is the module located? This is my first four wheel drive vehicle, and I absolutely love this SUV.