How do you reset engine check light on a 1986 olds cutlass 3.0 liter engine?

You can't simply "reset" the Check Engine light on a 1986 Olds Cutlass (or most older cars) like you can on many modern vehicles. Older cars don't have the sophisticated onboard diagnostics (OBD) systems that allow for simple resets. The Check Engine light (or possibly just a malfunction indicator lamp (MIL) in this case, as OBD-II wasn't mandated until 1996) is there to indicate a problem that needs to be diagnosed and fixed.

Instead of resetting, you need to *find and fix the problem causing the light*. Here's what you should do:

1. Locate a Diagnostic Trouble Code (DTC): Older vehicles often rely on blinking lights or patterns of the check engine light to give you a code. Consult your Oldsmobile Cutlass owner's manual. The manual should provide instructions on how to interpret the flashing light patterns to determine the problem. If your manual doesn't explain this, finding a service manual for your specific year and model is essential.

2. Use a multimeter (voltmeter): A multimeter can help you test various sensors and components that might be causing the issue (like the oxygen sensor, temperature sensor, etc.). This requires some automotive electrical knowledge.

3. Take it to a mechanic: This is the easiest and often most cost-effective solution, especially if you're not comfortable troubleshooting car problems yourself. A mechanic has the tools and knowledge to quickly diagnose the problem and fix it properly.

Important Note: Simply disconnecting the battery will *not* reset the check engine light on a 1986 Oldsmobile. It might temporarily clear it, but the underlying problem will still exist and the light will likely come back on. Ignoring the Check Engine light can lead to more serious engine damage.