Checking an engine by trial and error can be needlessly time consuming. Since your 1999 Mercury Cougar was manufactured after 1996, it is equipped with On-Board Diagnostics (OBD). As the OBD-II system runs routine tests, it catalogues problems. These malfunctions are grouped into two classes, pending codes and trouble codes. Once a "pending" problem is sensed often enough, the Cougar's computer will classify it as a trouble code, resulting in the service engine light coming on. Both types of codes can save a lot of time in the process of checking an engine.
Open the Cougar's driver side door and look beneath the dash. The Cougar's data link connection is located to the left of the steering column. It is a 16-pin receiving outlet that serves as an entry point to all of the vehicle's diagnostic scanners.
Plug your OBD-II scanner into the Cougar's data link connection.
Either turn the Cougar's electrical system on, or start the engine. Turn your scanner on, if your scanner is not programmed to auto-start once a connection is sensed.
Look at the codes on your scanner's screen. If they were not instantly and automatically retrieved, you will have to key in a retrieve command. Your scanner will differentiate between what is a trouble code and what is pending. Attend to the trouble codes first, as they caused the Cougar's service light to come on. If you do not have trouble codes, scroll through the pending codes. These could be anomalies, or they could be a sign of a developing problem.
Look up the codes in the scanner's manual. The code list should be found toward the back of the manual, either as a chapter or an appendix. The codes are universal to all OBD compliant vehicles. Mercury's supplemental codes can be found online. Once you have found descriptions for all the codes reported, you can start examining the engine in a more focused way.
- Ford owns Mercury, so if you are looking for manufacturer specific trouble codes, you might want to start your search with "Ford" as a key word, not "Mercury."
- Steps are a generic summation of how to use a code scanner, but brands differ, and so the process is slightly different for each scanner available. Some scanners turn themselves on, and some do not. Some require the engine running, and others do not. Always consult your manual for the exact instructions on how to retrieve codes.
- OBD Codes: Ford OBD Trouble Codes