Q: Check engine light after repair of alternator and leaky oil valve cover gaskets on a 2006 hyundai Tucson

Any one, or more, out of a list of thousands of OBD-II Diagnostic Trouble Codes could have caused your vehicle’s Check Engine Light to illuminate. Even though in your case the check engine light has come on immediately after specific repairs (i.e., the alternator and valve cover gaskets) no "one" of these many codes is any more likely than the others. Consequently, the only way to resolve something like this is in a check engine light diagnostic. During such a diagnostic, a certified mechanic from YourMechanic would use a code scanner to retrieve the specific diagnostic trouble code(s) from your car’s PCM that have caused the check engine light to illuminate. Using those codes, the appropriate individual vehicle components or sub-systems (often a sensor, circuit, and the like) are then tested to pinpoint the exact cause of the fault or the reason why the check engine light has illuminated. Once the faulty part or component is identified, it is explained to your satisfaction and the mechanic will let you know of the cost to repair. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.