How to Perform a Self Diagnostic Test on a 1999 Jeep Cherokee

1. 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.
2.
Fotolia.com'>
The test port is on the driver's side in most vehicles, but is sometimes on the passenger's side.
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.
3. Plug the scanner into the test port. Turn the ignition key 'On'. The scanner will come on automatically.
4. 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.