how to reset the check engine light
Not exactly sure how to reset the computer. I know on my car if you unhook the battery from the car and then reconnect it resets the system.
the light comes on when 1) the emmision excedes the 1.5 goverment standards, 2) component faliure, 3) or if the PCM can't "see" a component. so if the light is still on after a "fix" then you did not fix it, because the car will do a self test and if everything is correct then the light will turn off.
The light will not turn off by itself, it stores the codes for diagnosis even if the problem went away. To reset it disconnect your negative battery cable and step on the brake to make sure everything is discharged. Reconnect and it should be good, if the light comes on again, go get your codes read and you can visit MazdaWorld.org and we can help you solve the problem.
Sometimes Disconnecting the negative battery cable resets, but on newer cars you have to hook up a scan tool and clear the codes depending on the code that was set. some codes do not go away until so many drive cycles have completed which can take a long time. Some times that car has to run that test again and it has to pass it so many times before it goes away.
It could be fixed codes do not always turn off after you fix the component. the PROPER way to shut the light off is to clear the codes with a scan tool. if the light returns then it wasn't fixed.
Disconnecting the battery will not clear the codes, you need a scan tool. The ECM has an internal battery to keep the codes in case the battery gets disconnected. By the way, when the light comes on, that means your car has an emissions control issue, and that should be fixed, not cleared and ignored. Also, your car has almost 2000 different codes available, so it needs to be scanned to find the issue.
We are not talking about "most cars" we are talking about a Mazda Millenia in this case. I own one and know for a fact that disconnecting the battery and draining the capacitors will clear the codes the same way that clearing the codes with a code scanner would. Yes a CEL light does mean you have a problem that should be fixed but sometimes before fixing the problem you should clear the codes and see if the problem comes back and then diagnose the problem from there.
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