How to scan your vehicle with a generic OBD II code reader to diagnose the check engine light (CEL). How the code reader operates may vary between makes and models. OBD II was used on vehicles in the mid 1990s and newer. Before OBD II was the OBD I system which needs a specific reader for each vehicle.
Once the code is found, a simple internet search using your vehicle's make, model, and the code found will allow you to search what caused the issue, and what can be done to solve the problem. The internet search allows you to search the online database through car forums, online manuals, etc to help solve the issue.
If you have solved the issue causing the fault code and the vehicle does not clear the fault code, you may need to clear the code using a code reader. Or if you hate seeing the check engine light then you can clear it, but if the problem persists, you will need to fix the issue.