I just posted this for another person so as long as it's in memory, I'll share it with you too in case it will help your understanding:
There's well over 2000 potential codes, and only about half of them turn the Check Engine light on. Those are the codes that refer to something the could adversely affect emissions.
You can get an idea of the severity of a code by how the check Engine light acts. If the light turns on for a minor problem, it could turn off while you're driving if it's an intermittent problem and it goes away for a while. (The fault code stays in memory). If it's more serious but the problem goes away while you're driving, the light will stay on until you turn the ignition switch off and restart the engine. Then it won't turn on again until the problem occurs again. For even more serious problems that go away, the light will stay on any time the engine is running. The most serious is when the light is flashing. That means stop the engine right away because too much raw fuel is going into the exhaust where it will overheat and damage the catalytic converter.
Regardless of how the light acts, when a fault code is set, it stays in memory for a specific number of engine starts, or until it is erased with a scanner or by disconnecting the battery. The most important thing with intermittent problems is to read and record any codes before doing anything that will erase them because you don't want to lose that valuable information.
Tuesday, February 10th, 2015 AT 5:08 PM