from larry q...."If the ligth is on you need to check the codes to know what exactly is wrong--(check engine light)...how do you check the 'codes'....what codes?

If the light is on the computer sees a problem with the engine control system - It will log a code in its computer memory to help guide the technician where the problem lies. You need a special tool to access this inform ation to get "codes" In the US - Autozone usually does it for free.( Gets the codes for you )

You need to either buy a scan tool or take it to a place like autozone or advance. They can run diagnostics on it and give you a print out of the trouble codes. The codes are numbers stored within a car ECM when a problem is experienced. This in turn causes the light to come on.