1. Address the Underlying Problem:
* This is the MOST IMPORTANT step. The check engine light is illuminated for a reason. Ignoring it can lead to more serious (and expensive) engine damage.
* Get the code read: You need to know *why* the light is on. You can do this a few ways:
* OBD-II scanner: Buy a relatively inexpensive OBD-II code reader from an auto parts store. Plug it into the OBD-II port (usually under the dashboard) and it will read the trouble codes. These codes are crucial for identifying the problem.
* Auto parts store: Many auto parts stores will read the codes for free.
* Mechanic: A mechanic can diagnose the problem and provide a solution.
* Fix the problem: Once you know the code(s), research the problem online (be cautious about unqualified advice) or consult a repair manual or mechanic to fix the underlying issue. Only *after* the problem is solved should you attempt to reset the light.
2. Resetting the Light (After Fixing the Problem):
Once the problem is solved, there are several ways to try resetting the light. These methods will only work if the problem is resolved.
* Disconnect the battery: This is the simplest method. Disconnect the negative (-) battery terminal for at least 15-30 minutes. Reconnect the terminal and start the car. The light *may* turn off. This doesn't erase the codes from the computer's memory, but it may reset the light temporarily. The computer needs several driving cycles to determine if the issue is resolved.
* OBD-II Scanner: Many OBD-II scanners have a "clear codes" function. This is the most reliable method after fixing the problem, as it actually clears the trouble codes from the computer's memory.
* Driving Cycles: After repairing the issue, drive the car for several driving cycles (start, warm up, drive for a significant amount of time, turn off). The computer monitors the engine's performance, and if everything is fine, it will automatically turn off the light after a certain number of successful cycles.
Important Considerations:
* If the light comes back on immediately after resetting: The problem hasn't been solved. Don't keep resetting the light; find and fix the root cause.
* "Check Engine" vs. "Service Engine Soon": These are similar but can mean slightly different things. The same general principles apply, however.
* Repair Manual: A repair manual specific to your 1999 Oldsmobile Alero will provide detailed information and diagrams.
In short: Don't focus on resetting the light; focus on fixing whatever caused the light to come on in the first place. The reset is the last step. Ignoring the problem will likely lead to further damage and more expensive repairs down the road.
