Over time, your 1998 Cadillac Deville will encounter issues that will require you to spend time troubleshooting before you know what is causing them. By using the Deville's onboard diagnostic system, known as OBDII, you can find out what specific electrical or mechanical components are failing. Use an OBDII error code scanning tool to scan the diagnostic system for unique error codes that are sent out when components begin to stop working. When you know what specific parts are broken, you can begin the repair process sooner.
Find the location of the OBDII port by feeling around the area below your Deville's steering wheel. The port will be placed in the area above where your right knee would sit if you were sitting in the driver's seat. It is rectangular in shape and will be about two inches wide by three quarters of an inch in height.2
Plug the OBDII code scanning tool into the OBDII port and power the scanning tool on.3
Insert the key to your Deville into the ignition and turn the ignition so that either the engine is idling, or if the engine will not start, to the position before the engine starts. Either will activate the car's electronic system and prompt the code scanning tool to begin its error code scan.4
Take note of the error codes that appear on the display of the code scanning tool as the code scan is performed.5
Determine what the error codes signify by bringing the list to a local dealership, repair shop, or auto parts store, all of whom will have reference materials that can tell you what each error code represents. You can also perform a web search using a search engine to determine what parts are failing by looking up each error code.