How do you check if your check engine light is working?

 

there are various things that will trip a CEL...for instance...if you dont screw down gas cap tight enough the CEL will come on...or just unplug an O2 sensor that will trip a CEL too...just set up one of those situations and you will see if it turns on...if it does, then it works...then reset the ecu to turn off the CEL....

 

It'll come on for a second or two when you first turn the car on.