* ALDL (Assembly Line Diagnostic Link): This is the most common method for older GM vehicles. The ALDL connector is usually a rectangular port, often located under the dashboard near the steering column. However, its exact location might vary slightly depending on the trim level of the car. You'll need a method to read the codes from this port:
* Test Light: This is the most basic method. You'll need a test light and a wiring diagram (a repair manual is highly recommended). You'll connect the test light to specific pins in the ALDL connector while turning the ignition on and off according to a specific procedure. The flashing light will give you the trouble codes. This method requires some technical knowledge and can be tedious.
* ALDL Scanner: This is a much easier and more efficient method. A scanner designed to work with the ALDL system will connect to the port and directly display the trouble codes on a screen. You can find these scanners relatively inexpensively online.
* Check Engine Light (If Equipped): Some 1985 Eldorados might have a rudimentary check engine light, but it won't give you specific codes. If the light is on, it indicates a problem exists, but you'll still need to use the ALDL connector and a test light or scanner to diagnose it further.
Important Considerations:
* Repair Manual: Having a factory repair manual for your specific 1985 Cadillac Eldorado is invaluable. It will show you the exact location of the ALDL connector and provide detailed instructions on how to retrieve and interpret the diagnostic trouble codes (DTCs).
* Year-Specific Information: The specifics of the diagnostic system can vary slightly even within the same model year. Always refer to a repair manual specific to your car's year and model.
* Professional Diagnosis: If you're not comfortable working with automotive electrical systems, it's best to take your car to a mechanic specializing in older vehicles. They will have the tools and expertise to properly diagnose the problem.
In summary, while modern OBD-II systems simplify this process, older cars like your Eldorado require a more hands-on approach using the ALDL port. A repair manual and either a test light or a dedicated ALDL scanner are crucial for success.
