Q: In a 2005 Lexus es330 How do you turn off the check engine light once fuel cap has been replaced and is on securely?

Hi there. Unfortunately, a plug & play code reader cannot determine the fault that has set the check engine light. The codes that the parts person pulled are most likely what are called evaporative emissions codes ( these codes pertain to the system that controls fuel vapors). This system includes all hoses and connections from the gas cap to the fuel tank to the engine. A proper diagnosis inspection is required to accurately diagnose the fault that caused the stored codes. When the engine computer detects a fault (a reading that is out of specifications) it stores a code and illuminates the check engine light. However, the computer does not know what caused the fault; it performs a test and the test failed. I strongly suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several available technicians that can assist you with a [check engine light inspection}(https://www.yourmechanic.com/services/check-engine-light-is-on-inspection).