A normal 16-pin Data-Link Connector OBD-II is on some '95 vehicles and most '96-present vehicles. On Board Diagnostics (OBD) has been around for awhile, but hasn't been mandated in any way til vehicle model year 1996. OBD-II vehicles store codes in their computers and must be retrieved with a scanner or a code-reader. A Diagnostic Trouble Code (DTC) is made up of 5 digits. Look below: There are two types of DTC's -- Type A and Type B: Type A Emissions related. Requests illumination of the MIL after one failed driving cycle. Stores a freeze frame DTC after one failed driving cycle. Type B Emissions related. Sets a Pending Trouble Code after one failed driving cycle. Clears a Pending Trouble Code after one successful driving cycle. Turns on the MIL after two consecutive failed driving cycles. Stores a freeze frame after two consecutive failed driving cycles. This is by far the best code description layout I've seen for OBD-II systems (PDF File): East Coast EFI Codes The following link is to obd-codes.com which shows Fords Manufacturer Specific codes: Ford Specific Codes There are four types of codes, Powertrain (P), Body (B), Network (U), and C (Chassis) The most common is Powertrain.