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Premium,ExMod 2000-03
NW Illinois

1 recommendation

reply to weston631

Re: Check Engine Light - Knows very little about cars

If the light comes back on, then yes, it needs to be addressed. As I noted, a proper diagnostic needs to be completed that will isolate the nature of the problem.

As far as when it will come back, that is up to the situation at hand; No problems present to cause the light to come on again, then it won't be back on at all, at least for that particular problem. The more significant the issue, the faster it comes on. For example, an engine misfire that is detected will immediately cause the light to come on, and if it is a persistent misfire, the light will actually flash to signify "take care of this NOW!". This is because a persistent misfire condition can cause damage to the catalytic converter, as well as cause excessive tailpipe emissions in the form of raw, unburned fuel.

Other problems that are less critical and non-damaging may take several "detection cycles" to set a trouble code and turn on the light. If the problem is detected over a certain number of start-stop cycles, or for a certain length of time, it will come on. Then there are codes that will be set in the computer but don't cause the light to come on at all. Typically these will be body-control module issues, and some drivetrain scenarios that are out of range. They are detectable only when a technician performs diagnostics, and then they can be addressed if needed.

There's a quick and basic explanation of the Check Engine Light display strategy.