Your car has many computers that monitor your engine for the best performance, your transmission for proper shifting, your braking system for safe stopping, and it monitors many other devices to make sure they are working properly. If a system detects a problem, it needs to alert you, so you can bring the car in for service. This is the role of the check engine light.
The check engine light looks different from car to car. It is usually a yellow or orange color. It will rarely be red. Most of the time it illuminates in the shape of an engine. If the check engine light comes on solid (not blinking), you can continue to drive the car until you have a chance to bring it in. This does not mean you should ignore it.
When the check engine light is on, the car defaults to a backup system that controls all the important systems. Driving around for a short time until you can set up an appointment is no problem, but continuing to drive more than 20 miles is a bad idea.
If the check engine light is blinking rhythmically, this indicates a serious problem! A computer system has had a major malfunction that will damage the catalytic converter. If you notice a blinking check engine light, you do not need to stop in the middle of the bridge and call a tow truck, but you do need to stop driving as soon as it is practical. Whether the check engine light is solid or blinking, it's a good idea to drive gently.
The modern car is more complex than ever, and many folks believe a small hand-held code reader will tell you what’s wrong with the car. This is incorrect information. It is called a code reader for a reason; it reads the trouble code for the major systems only. A code reader will not tell you the complete story of the car’s condition.
Please don’t diagnose or replace parts based on a code reader device. The only way to correctly find all the issues with your car is to use a scanner. The scanner does what it says; it scans all the modules and systems of the car, instead of a select few that a code reader does. Most cars have 20 to 100 modules; a code reader is not set to read even half of those.
No one wants to pay for expensive testing, but it beats changing parts and losing that hard-earned cash we all want to spend elsewhere. Please use a shop that is well equipped and don’t rely on the old code reader any more.