There's no single button or process to "reset the service system." The method depends on what specific reminder you're trying to reset. It's very likely a simple odometer-based reminder.
Here's what you'll probably need to do:
* Check your Owner's Manual: This is the most crucial step. Your owner's manual will explicitly describe how to reset any service indicators or reminders your car might have.
* Look for a Trip Odometer Reset: Many cars use the trip odometer as a way to track maintenance intervals. If you're tracking oil changes or other services based on mileage, simply resetting the trip odometer might be sufficient. This is usually done by holding down a button on the instrument cluster while turning the ignition on (or maybe while the engine is running). Consult your manual for specifics.
* There's no "Service Engine Soon" light: Unlike newer cars, 1991 Cadillacs don't have an electronically-controlled "Service Engine Soon" (SES) or "Check Engine" light that requires a specific diagnostic tool for reset.
In short, there's no universal "CCR system reset" for your car. You need to consult your owner's manual to understand the specific maintenance reminders your car uses and how to reset them. If you don't have the owner's manual, try searching online for a digital version specific to your 1991 Cadillac Eldorado.
