The 1999 Jeep Cherokee is equipped with an on-board diagnostic center, also called the OBD. The '99 series has the second OBD system, also known as OBD2 or OBD-II. This system is more sophisticated than the original OBD, which was created in the 1970s and early 1980s primarily to monitor car emissions. The OBD-II in the 1999 Jeep monitors all parts of the Cherokee's functions, including the chassis, accessories and body. Running a self-diagnosis highlights the Cherokee's problem areas so they can be easily identified and fixed.
Park the Jeep in a well lit, level area and turn off the engine. The diagnostic sequence won't activate while the engine is operating.
Locate the test plug-in. It's a small, square electrical port found under the driver's side dash. Pry off the plastic cover, if it has one, to expose the ports.
Plug the scanner into the test port. Turn the ignition key "On". The scanner will come on automatically.
Follow the prompt on the scanner to retrieve the diagnostic codes stored in the Jeep's computer. Write down the codes that appear and check their meanings in your service manual.
