Cadillacs manufactured after 1996 use the second wave of On-Board Diagnostic fault codes. The Cadillac's computer runs a series of routine checks and monitors the health of the system. Once a malfunction has occurred the computer will issue a fault code and activate a warning light on the dash. Cadillacs before 1996 use an OBD-I coding. The vehicle can also perform a self diagnostic if you use a jumper wire to connect the self-test ports under the hood.
Place your key into the Cadillac's ignition but do not sit in the driver's seat. Leave the key unturned. Leave your scanner's user manual in the driver's seat.
Find the data-link-connection outlet beneath the dashboard; location depends on the model of Cadillac. A 2008 CTS has its DLC port to the far right of the steering wheel's underside. A 1999 Catera features a DLC right under the steering wheel.
Connect the OBD-II scanner's cable to the DLC outlet. The cable features a 16-pin plug that will fit the DLC's 16 receptors.
Turn the key in the Cadillac's ignition to start the electrical system. Do not crank the engine.
Look at your scanner; a diagnostic fault code should be on the screen. Some scanners, do not automatically switch themselves on when they sense a connection to a diagnostic system. If you own one of these scanners, press the power button. The fault code will appear in a few seconds.
Consult the scanner's user manual. It will contain the diagnosis of a problem and definition of generic fault codes. Cadillic has supplemental fault codes unique to its models. Your user's manual will likely not have these codes, and they may not be in the Cadillac's owner's manual. There are free resources online that list manufacturer fault codes.
