Check engine light on

That light has nothing to do with fluids. Your engine computer can detect over 2,000 different problems. When it does, it sets a diagnostic fault code, then if that problem could adversely affect emissions, it turns on the check engine light. The place to start is by having the fault codes read and recorded. They will indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. The people at many auto parts stores will read those codes for you for free.