How do you fix a check engine light?

To fix a check engine light, start by using an OBD-II scanner to read the diagnostic trouble codes (DTCs) stored in the vehicle's computer. Address the specific issue indicated by the codes, which could range from a loose gas cap to more serious problems like a faulty sensor. After repairs, reset the check engine light either through the scanner or by disconnecting the battery for a short period. If the light remains on, further diagnosis may be needed.