Obtaining an OBD (on-board diagnostics) code for a 1994 Jeep requires a diagnostic terminal or scanning tool capable of interfacing with the OBD1 style on-board computer installed on this model of Jeep. You'll hook the scanning tool to the assembly line diagnostic link (ALDL), which is located under the hood of a 1994 Jeep. If you don't have an ALDL-to-USB cable capable of plugging into your computer and software that can read the diagnostic codes, you can decipher the codes using a paper clip and the Internet.
Locate the ALDL connector. It is a black L-shaped connector near the battery.
Hold the connector with the curved part of the head facing down.
Place the paper clip in the ground (terminal A), which is the farthest on the top right.
Place the other end of the paper clip in the diagnostic terminal (terminal B) which is right next to the ground on the left.
Turn the key in the ignition to the "run" position but do not start the car.
Watch the check-engine light flashes to obtain the codes. The first code is usually one long flash followed by two short flashes, indicating the number 12. Once you have the OBD1 numeric codes, you can look them up on the Internet to obtain the meaning of the code. For example, 12 means system normal, 31--three long flashes and one short flash--means there is a cam position sensor fault. There are a number of websites dedicated to helping do-it-yourselfers determine what the numeric codes mean (see references and resources).
