Check Engine Light: Watch Your Vehicle’s Warning System to Avoid Costly Repairs


If your “Check Engine Light” comes on, bring your vehicle in as soon as possible. We have all the latest tools to diagnose the issue and get you back on the road quickly.

We’re here today with Robert Lugo of Doctor of Motors, talking about auto maintenance and what you need to know about maintaining your car. Robert, let’s talk about the check engine light today. Why does the light come on in your vehicle? When that comes on, what does it mean?

Robert: Well, pretty much the computer, or the vehicle, has only one way of telling you that something is wrong. And the computer has anywhere from 5,000 to 8,000 different codes, which are different areas of the vehicle that are having a problem.

Host: Five thousand?

Robert: Yes. So when that happens, that’s the indication for you to get ready to find the nearest shop.

Host: Does it have anything to do with tune up?

Robert: Tuning…vehicles these days are all computer controlled. So there’s not necessarily tuning. The computer tunes it to its most optimal running settings at all times. If there’s something that’s out of whack that it can’t control, then it turns that light on to say, “This is beyond my limit” and send it in to fix it.

Host: So the computer tries to control the vehicle, but if it gets beyond the capacity of the computer to self fix…

Robert: Definitely, oh, definitely.

Common Check Engine Light Errors

Host: Then the alert comes out. So what would be some examples of the…what errors do you see most commonly?

Robert: One of the most common things that I see is…you’ll be driving down the road and the check engine light starts to flash. This is an indication that the computer has already done everything that it can to lessen the amount of fuel going through the engine so that it won’t burn as hot.

And to get even more technical about it, what’s coming out of the exhaust needs to be as clean air as possible. So smog rules, what they’ve stated, is that there needs to be as little amounts of carbon monoxide, any combustible, any type of fuel whether it be oil, or fuel coming through there. So you have a catalytic converter. That catalytic converter…its job is meant to burn whatever the engine wasn’t able to burn. That’s what it comes down to.

Now, the computer is constantly monitoring that catalytic converter by what’s going into it and what’s coming out of it. And if too much fuel is going in then the computer tries to help out by giving the engine less fuel. Well, when there’s a problem, what will happen is that too much fuel is going through, the catalytic converter doesn’t care if it’s a lot or a little. It just does its job. And it will do it until it kills itself because that’s how the car is manufactured.

So what happens is the reason why that light comes on is because the computer is monitoring the temperature of the catalytic converter and when it gets too high, as in it’s starting to melt or to damage it in some way, then that light flashes and that means stop.

Host: Stop the vehicle?

Robert: Stop the vehicle, pull over, and get it to a shop.


Host: Are the signals coming from the lamp, the light on the dashboard, are they consistent between brands of cars, or is every car different?

Robert: There are rules and regulations saying that they have to be the same because you shouldn’t have to, whether you drive a Ford or whether you drive a VW, you shouldn’t have to know these things. It should be generic.

Evaporative Emission System Errors

Host: So other than, say, the fuel mixture has gone wrong, what other sorts of errors pop up commonly?

Robert: One of the other most common ones is evap codes.

Host: What does that mean?

Robert: Evap is evaporative emmission system. To make that as simple to understand is you have your gas tank, the bottom half of the gas tank is the liquid, the top half is the vapors. They want those vapors to be controlled and pulled into the engine and burned, just like they would fuel.

All of this is to keep our atmosphere nice and clean and healthier, just like Los Angeles. If you’ve seen there, the smog has really gone down in the last 20 years. They’ve done a great job.

Host: A remarkable change. Much better.

Robert: Yes, but it’s taken a lot of work and us all working together with these cars to make this happen.

Fasten Your Gas Cap Tightly and Do Not ‘Top-Off”

Host: I didn’t know that. So the vapor in the tank is actually part of the system as well, in the gas tank?

Robert: Yes, you expend more damaging fumes into the atmosphere when you’re getting gas than when you’re driving the 400 miles that it takes to empty that gas.

Host: Which is why they say, always push the nozzle completely onto the connection.

Robert: They say, “don’t top off”.

Host: Okay. And, Robert, so if I let that light just stay on, what are the possible consequences? It sounds like it could be serious to the engine. So is it just a smog control and performance issue, or is there something that could happen that’s potentially damaging to the engine itself?

Robert: Well, there’s really no way to tell unless you take it to a professional and say, “Hey my check engine light came on. Can you test it?” The thing is, you’re not going to know if it’s something minor that’s okay to let sit for a little while or if it’s a big problem.

If you let it stay on for a year, the car will probably still drive because its main purpose is to get you from point A to point B. But you don’t know when there’s a problem and you’re not going to know when there’s a problem if you don’t get it addressed.

Host: So the best practice is to go to a shop that you trust as soon as possible.

Robert: Correct.

Host: And Doctor of Motors has the diagnostic equipment to do that?

Robert: All the latest equipment to do that, yes.

Check Engine Lights and Smog Tests

Host: All the latest equipment. If the check engine light is on, is it ever possible to pass a smog check or is that an automatic fail?

Robert: That is an automatic fail. Now, as far as smog regulations, shops are not allowed to ask you if that check engine light is on. There’s a lot of weird rules they have. It’s one of those things that they’re not allowed to ask you. So the more honest you are with the smog shop when you let them know. If you tell them, “Hey, I just had my battery replaced,” or if it was just in for an oil change, let them know. The shops are here to help you to figure out if you’re ready for smog because no one wants to waste their time.

The shop doesn’t want to waste your time and you don’t want to waste the shop’s time because you wanna get in, get your smog, and get out.

Resetting the Check Engine Light

Host: Sure. Is it possible to reset the light yourself and is there any reason you would ever want to do that, or is that just a bad idea?

Robert: There is ways to do it. One thing is disconnecting the battery, letting it sit for anywhere from 10 minutes to 30 minutes. Of course, this is not recommended because it causes other issues.

Host: What issues?

Robert: Well, just the other day, someone came in and they had replaced their battery and their radio has said “code” on it. What that means is that the battery was disconnected without properly supplying power to the computer and so their radio lost its code, which means it thinks it was being stolen. So now to get that code back, either you look in the glove box for a card that came from the factory saying, “This is your radio code,” but people lose it. It happens. So what then happens is you need to have the radio removed and get the serial number off the radio.

It’s a process. It’s a process that you just don’t need to deal with if you just got the battery replaced by someone who knew what they were doing.

Host: So best practice on check engine lamp or light is if you see it coming on for any reasons, get into the shop straight away.

Robert: As soon as you can.


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