Engine light

There arewell over 2,000 defects the engine computer can detect. About half of them refer to things that could adversely affect emissions. Those are the codes that turn on the check engine light. A leak in the fuel vapor recovery system, including a loose gas cap, is just one of those potential leaks.

The place to start is by having the diagnostic fault codes read and recorded. Those will indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. Fault codes do not say to replace parts or that one is bad. A part could be defective, but first we have to rule out wiring and connector terminal problems.

The people at many auto parts stores will read those codes for you for free, but they usually can only read fault codes in the engine computer, not the many other computers on your car.