The Check Engine light — is a signal from the car's engine computer that something isn't right. If there is any change in the car's performance, any mechanical noises, smoke from the tailpipe or electrical smells, stop the car and call for immediate assistance. If there are none of these symptoms, restart the car and if the light maintains on then you'll need to visit a mechanic to diagnose the problem.
Car's made after 1996, have a standardized system under a protocol called OBD-II, which stipulated a standardized list of diagnostic trouble codes (DTC) and mandated that all cars provide a universal connector to access this information. It's usually located under the steering column and is easy to access, if you take your car to any mechanic they will have a code reader that connects to this standardized on board diagnostics (OBD) port and transmits a code to diagnose the problem. For more information about engine light coding there are helpful websites such as Engine Light Help.
CarMD published a list of the five most common Check Engine light codes:
- O2 sensor (part of the emissions system, monitoring and helping adjust the air-fuel mixture)
- Loose gas cap
- Catalytic converter
- Mass air flow sensor (monitoring the amount of air mixed in the fuel injection system)
- Spark plug wires