What should I check on my vehicle before using the Code Reader?

Before performing any tests, you should check engine oil, power steering fluid, transmission fluid, and coolant levels; ensure the air filter is clean; verify all engine belts are in good condition; check rubber and steel hoses for leaks or damage; ensure spark plugs are clean and spark plug wires are properly connected; verify battery terminals are clean and tight with proper voltage; check all electrical wiring and harnesses for proper connection; and ensure the engine is mechanically sound with proper compression and vacuum.