Why is the check engine light so important?

Why does the check engine light come on all the time on cars and trucks? Should i ignore it?

It comes on to tell you that something is wrong… i.e. Check the Engine That is why it is there. That should be obvious. If it isn’t, read your owners manual and it will tell you the same thing.

If you ignore it, more serious damage can occur, plus, your car will not pass emissions inspection if your state has one.


Well, that depends. Would you ignore if your body had a fever? No? Then you probably shouldn’t ignore your check engine light. It’s basically like a fever for your car and lets you know that something is wrong. Many auto parts stores will check to see what code it’s throwing for free. Those codes will give you some idea of what needs to be replaced and/or fixed.

First, you are laboring under a misapprehension if you think that it is common for vehicles to have their CEL lit up. That light is your signal that something is amiss with the ignition system, or the emissions system, or the fuel delivery system. If a car is well-maintained, that light might never start to glow, and if a problem is repaired promptly, the light shouldn’t be “on” for an extended period of time.

I have had 5 cars that were equipped with a CEL, and only one of them ever had the CEL light up. In that case, the car was less than 1 year old, and I drove to the dealership immediately. It turned-out that a solenoid in the evaporative emissions system had gone bad, and they had me back on the road in less than 1 hour–gratis. In the ensuing 10 years that I owned that car, the CEL never lit-up again.

Modern vehicles are incredibly complex, and without OBD technology and the CEL, it would be possible to cause a lot of expensive damage to that vehicle if the owner was not aware of certain malfunctions. The CEL is an important feature on all modern vehicles, and it is vital that it not be ignored for an extended period of time if one wants his/her vehicle to run at its optimum.

1 Like

I agree with everything that VDCdriver said. I think I’ve seen a check-engine light twice in the past 20 years. In addition, some of the issues that light up the check-engine light can reduce your fuel economy, so ignoring it could be costing you money.

I hope you’re aware that you need to stop driving immediately if the light starts to flash.

I doubt the OP will ever return but is it possible that all the lights come at starting has them confused.

1 Like

For most people, it is a fairly rare occurrence.
I think that it is a part of human nature for a person to assume that everyone has the same problem, and I think that this sort of denial of reality is a defense mechanism to help one feel better about his/her own problem.

And, it is certainly not limited to cars. In my role as a school counselor, when I would try to engage parents in conversation about their child’s substance abuse problem, or their child’s ongoing run-ins with the local cops, more often than not, those parents would inform me that “ALL of the kids are taking drugs”, or “EVERY kid has an arrest record by 11th grade”. Of course, these people were dangerously wrong, but I guess that–in the short term–they felt better by kidding themselves about the reality that they had to deal with.

In general, no.
There are some problems that trip the CEL that “could” be ignored if you’re looking for an example, like a faulty downstream O2 sensor.
The problem with ignoring it, however, is if a second problem arises, you would never know it, since your CEL is already lit.

If your state has emission checks, then a lit CEL will need to be addressed.

Some vehicles (like Toyota) - if CEL is on then ABS and traction control is OFF. It automatically disables ABS and traction control for ANY CEL condition.

It is not uncommon for me. The CEL has been on my 08 Yaris for the last 150,000 miles. I check it periodically but it is the same downstream 02 sensor. That does nothing but tell me if the cat is not working properly. I bought a new 02 sensor about 150K miles ago but never got around to changing it. I have had numerous cars that have the 02 sensor on. My 99 dodge it would be on but non of the dash panel works thanks to a rodent. It is seldom used so as long as it runs fine I am not worried. The thing that sucks the most is guessing on how much fuel is left. I really like riding my old choppers with zero gauges. No oil pressure, no fuel gauge, no volt meter, nothing. You just listen to the hum of the engine to tell if it is running fine. When something is wrong, it will let you know.

I’m glad that works for you, but that is pretty horrible advice to tell someone. A check engine light staying on likely means your emissions system isn’t functioning properly. If you live somewhere where this is tested on a periodic basis- it is cheaper to get it fixed as soon as possible, rather than waiting til other systems get fouled by that first issue.
Also, in many jurisdictions, a car can not be registered if the Check Engine light is on. as this is also a periodic event, this issue needs to be taken care of.

this doesn’t even touch the environmental impact of an improperly tuned car putting emissions into the atmosphere that we all have to share.

all in all- telling someone to wait for funny sounds to fix something that could easily be fixed before a breakdown is very poor advice.

1 Like


Without question!

I have no inspections nor registration issues. I am so glad I don’t have to deal with that headache. If you have title, insurance, and valid plates you can drive it.


I don’t either but in all 3 of my cars, the CEL is off. Downstream O2 sensors and all.

Do you do any kind of PM? CEL light is like a PM. Fix it BEFORE there’s a major problem.

1 Like

It’s designed into the car you purchased to let you know the computer thinks something seems to be wrong, particularly when the putative problem is with the emissions affecting systems. If nothing else, when drivers see it and take their car to the shop for a look-see, it helps reduce air pollution a little. That light has never turned on in my 27 year old Corolla. With newer cars (post 1996 or so) there’s more stuff in them that can go wrong, especially in the emissions evaporative system, so those cars tend to turn the CEL on more often. That light is often ignored, but ignoring it is at your own wallet’s peril. For example if there’s an air fuel mixture problem causing it to turn on, continuing to drive can ruin the very to expensive to replace catalytic converter. In some cases once you know what’s causing it, if short on funds you can ignore it. The problem with this however is that if something else goes wrong you won’t know it, b/c the light is already on. So if you ignore it, you should check the codes every few weeks still.