Check Engine Light

There's over a thousand diagnostic fault codes that can be set in the Engine Computer. About half of them relate to things that can cause an increase in emissions and those are required to turn on the Check Engine light. Your mechanic will start by reading the codes. They will indicate the circuit or system that needs further diagnosis.

If you ignore the Check Engine light for a month after it goes off the stored codes will likely erase automatically and that valuable information will be lost. You must have the codes read right away before that happens.