Why is My gmc Check Engine Light On?

Your  Gmc check engine light came on, now what? These tips can help you determine whether your vehicle has major engine problems or just a loose gas cap.

We’ve all been there before. You’re driving along when you notice a yellow light out of the corner of your eye. A quick glance at the dash confirms your fear. It’s the check engine light. If you’re like most car owners, you’re not sure if you should continue to panic or not, and you have little idea what that light is trying to tell you or how you should react.

The often misunderstood check engine light or “service engine soon” message can mean many different things. It could be a misfiring engine, a broken oxygen sensor or simply a loose gas cap.

When you see the check engine light it doesn’t necessarily mean you need to pull the car over to the side of the road and call a tow truck. It does mean you should get the car checked out as soon as possible. If you ignore the warning, you could end up causing further damage. It could also be a sign that you’re getting poor fuel economy and emitting high levels of pollutants.

In any case, if the check engine light is on in your car, it’s time to schedule a service appointment. At our service center, we have factory-trained technicians who can easily check and diagnose what’s behind your check engine light message, at a cost that is nearly always lower than a private garage.

Gmc Engine Check Light

gmc Check Engine Light

A flashing light means that the problem is serious and that if it isn’t fixed right away, it could cause a lot of damage to the car. If the check engine light on your GMC starts flashing, it means that something is wrong and needs to be fixed right away.

You should bring your GMC in right away. This blinking light usually means that the engine is misfiring badly, which lets unburned fuel go into the exhaust system. There, it can quickly raise the temperature of the catalytic converter to a point where damage is likely and an expensive repair is needed.

Some owners ask if the check engine light flashes because of the spark plugs. This could be the reason for sure. Misfiring can be caused by a bad, old, or dirty spark plug.

If you ignore the problem or keep driving, it can spread to the spark plug wires, the catalytic converter, or the ignition coils, which can be very expensive to fix.

Also Read: Factors Why Your Volkswagen Check Engine Light is On


There are a lot of things that could cause the Check Engine Light to come on, but after years of providing Check Engine Light Diagnosis Service, we know that there are a few common ones, like a loose gas cap.

Other common reasons for a Check Engine Light are a problem with the fuel injection system, a broken oxygen sensor, a broken emissions control part, a dirty mass airflow sensor, a broken head gasket, or broken spark plugs.

No matter what is causing the Check Engine Light to come on, we have the GMC Certified Mechanics and the certified service protocol to find the source of the problem and fix it as needed to bring it back to factory standards.

When this happens, the Check Engine Light turns off, and you know that the problem with your GMC has been fixed and you can leave the service centre.

Every GMC was made with a high-tech performance monitoring system that includes a computer and a set of sensors placed in key places around the car to check on its most important systems.

The sensors are always looking at the environment and sending information to the electronic control unit. If the electronic control unit sees that the data is not within factory limits, the Check Engine Light will come on to let you know there is a problem.

But that’s the problem with the Check Engine Light: it won’t tell you what’s wrong or what to do about it. That’s where we come in. Coggin Buick/GMC of Orange Park offers a Check Engine Light Diagnosis Service that finds the root of the problem and gives you advice on what to do next from a highly qualified service professional.


The check engine light is one of the most commonly misunderstood lights or indicators on your GMC. The check engine light is part of the onboard diagnostics system and can show up in a few different ways.

It could say “Check Engine,” it could be a picture of an engine, or it could be both. This light can be either yellow or red, and it is part of the diagnostics system in your car. Since the 1980s, onboard computers have been used more and more to control and monitor how a car works.

They can do a lot for your GMC. Some of these are controlling the speed of the engine, the timing of the ignition, shifting automatic transmissions, and setting up stability control, just to name a few. So, you should know that the check engine light can mean a lot of different things.


If the problem or code that made your GMC’s check engine light come on is fixed, the light will usually turn off by itself.

For example, if your check engine light came on because your gas cap was loose, tightening it will turn off the light. Still, if your catalytic converter is still working and you did a lot of stop-and-go driving, the check engine light may have come on because the converter was used so much.

Most of the time, your GMC light will go out between 20 and 40 miles after you’ve driven. If you drive over that amount and the light is still on, you will need to bring it to Coggin Buick/GMC of Orange Park so the light and code can be checked again and reset.


What do you do when you’re driving your GMC and all of a sudden a yellow light that says “Check Engine” comes on? If you’re like most GMC owners, when that light comes on, your heart sinks a little because you don’t know what it means or what to do.

Just as stressful can be the fear of the unknown or the cost of the unknown. But take a deep breath and remember that just because the light is on doesn’t mean you have to pull over to the side of the road and call a tow truck.

Instead, you should get your GMC checked as soon as you can. If you ignore that warning, it could hurt expensive engine parts in a big way.

When your GMC’s onboard computer, the electronic control module (ECM), finds a problem in the electronic control system that it can’t fix, a computer turns on your check engine light.

This amber or yellow light usually says “Check engine” or “Service engine soon.” Sometimes, the light is just a picture of an engine or the word “check” next to a picture of an engine.

When the light comes on, the ECM stores a “trouble code” in its memory that tells what the problem is, whether it’s a sensor or a broken part of the engine. Our GMC auto repair mechanics at Coggin Buick/GMC of Orange Park use an electronic scan tool to read this code.

If you want to do it yourself, there are still a number of code readers that aren’t too expensive and are made for that. Even though this code will tell you what the problem is, only a trained professional can really figure out what is wrong and fix it.

Gmc Check Engine Light Codes

When the check engine light comes on, it can be scary to see that little light on your car’s dashboard light up all of a sudden. However, you shouldn’t run away in fear right away.

If you hear the term “diagnostic trouble codes” (DTC), it just means “check engine light codes.” These are computer codes for cars that are kept by the ECM, also called the OBD (on-board computer diagnostic system) in your car.

There are a lot of different things your check engine light can mean. Even though that sounds hard, if you take the time to do some basic diagnostics, you’ll learn useful things about your car and be able to use the Check Engine Light as it was meant to be used: as a guide.

Sadly, the Check Engine Light doesn’t always go on with clear and helpful signs that something is wrong with a car. Since there are hundreds of possible OBD codes, there are also hundreds of reasons why the light might be on, such as:

  • Gas Cap Loose or Not There Gas Cap Bad Spark Plugs
  • Transmission issues
  • Problems with the old battery ignition system
  • Computer output circuit issues
  • O2 Sensor Emissions controls issues
  • Fuel and air metering systems problems

Reasons Why Your Gmc Check Engine Light On ?

If your car’s check engine light comes on, you might just need to tighten or replace the gas cap.
Again, the check engine light could be a sign of a serious problem that could damage your engine and cost a lot of money to fix.

Depending on what kind of car you have, the check engine light will either be on or blink.
Most of the time, a steady glow means something less serious, but a flashing check engine light means that your car’s engine is in serious trouble and needs service right away.

If your GMC’s check engine light is flashing, you should not drive it and should get GMC service as soon as possible. Here are the most common reasons why your check engine light might turn on:

Your GMC needs new spark plugs and/or plug wires.

The spark plugs are what light the air and fuel mixture in your car’s combustion chamber on fire. The pistons move because of this explosion, which makes the engine work. The ignition coil sends the spark to the spark plugs through the spark plug wires.

If your spark plugs or spark plug wires are broken or old, your car won’t run as well and won’t have as much power. In the worst cases, your engine won’t start or will have trouble running.

If the spark plugs and plug wires are worn out, the catalytic converter can get clogged or the ignition coils and O2 sensors can get damaged, which will cost more to fix.

Your catalytic converter is broken or is about to break.

The GMC’s exhaust system includes a catalytic converter. The job of the catalytic converter is to change the carbon monoxide that is made during combustion into carbon dioxide.

Most of the time, poor maintenance is to blame for a broken catalytic converter. This is why Coggin Buick/GMC of Orange Park offers a free multi-point check with every GMC service.

If your catalytic converter is broken and you don’t get it fixed, your GMC won’t pass an emissions test, the engine won’t run as well, and your fuel economy will go down.

Your car may also run hotter, which can cause other problems besides just overheating.

The gas cap on your GMC is loose, broken, or missing

The gas cap on your GMC does a lot of different things. It keeps gas fumes from escaping when you’re not driving, seals the fuel system, and helps keep fuel tank pressure steady.

What will happen if the fuel cap is broken? If your gas cap is old or the seal has been broken, you could lose gas through evaporation, which would mean you have to go to the gas station more often. Luckily, it doesn’t cost much to replace a gas cap.

If your GMC’s check engine light comes on quickly after you put gas in it, the first thing you should do is make sure the gas cap isn’t loose or that it’s still on the car’s roof or at the fuel pump.

Your MAF, which stands for mass airflow sensor, needs to be changed

The mass airflow sensor in your GMC measures how much air is going into the engine to figure out how much fuel it needs to run efficiently.

The mass airflow sensor is a part of the engine management system. It helps the engine adjust to changes like altitude.

If your GMC is hard to start, runs rough, or the throttle pedal moves suddenly, this could be a sign that the mass airflow sensor is broken.

Your GMC has a vacuum leak

Every GMC has a vacuum system that does a lot of different things.

Again, the vacuum system helps cut down on harmful emissions by directing the fumes that come out of the engine when gasoline evaporates.

If your RPM is high at idle or goes up and down randomly, it could be because of a vacuum leak.

Vacuum hoses can dry out and crack over time, especially if they are exposed to very hot or very cold temperatures.

The battery is dead or almost dead.

Your GMC can’t work without its battery. Without a battery, your car won’t start, it won’t light up the road in front of you, it won’t play the radio, and it won’t charge your phone.

Batteries for cars today last a lot longer than they did a few decades ago, and they don’t really need to be taken care of.

The price of a new one depends on what kind of GMC you drive, but you can check out our coupons and specials for service.

You need to get a new O2 Sensor (Oxygen Sensor).

The Oxygen sensor, also called the O2 sensor, checks how much oxygen is in your exhaust system. If there is too much oxygen in your exhaust system, your fuel will burn faster and your car will use more gas. If I don’t replace your O2 sensor, what will happen? A broken sensor can not only change how many miles per gallon your car gets, but it can also hurt your catalytic converter and the spark plugs in your GMC. The O2 sensor sends information to the car’s computer so that it can figure out how much air and fuel should go into each cylinder. Again, an O2 sensor that doesn’t work right can cause a car to fail an emissions test.

any problems with aftermarket items.

If you don’t know what you’re doing, an aftermarket alarm, exhaust, or other part can mess up your GMC. These add-on parts and accessories can drain the battery, turn on the check engine light, or even make the car impossible to start. If these problems sound familiar, bring your car to GMC and our team of certified mechanics will make sure that your aftermarket parts were installed correctly and aren’t causing any problems. Getting accessories, especially aftermarket parts and accessories, or using OEM parts from the beginning might cost a bit more, but it could save you money if you don’t have to pay to fix bad work or damage caused by bad installation.

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