Can A Bad Alternator Cause Check Engine Light [Explained]

If the check engine light in your car has come on and you have a faulty alternator at the same time, you may think that the alternator has caused this issue. So, can a bad alternator cause check engine light?

The answer is both yes and no. It’s not common for a bad alternator to throw a check engine light but it can happen in a few cases. Keep on reading to find out all about it in detail.

can a bad alternator cause check engine light

This guide is jampacked with information as we’ll also discuss what are the more common reasons behind a check engine light and how you can tell if your alternator is bad. Without further ado, let’s jump in!

Can A Bad Alternator Cause Check Engine Light [Know It All]

The alternator powers the electrical system in your vehicle and also charges the battery when the car is on the move. It’s an important component that can cause a plethora of issues with your vehicle when it goes bad.

Generally, the alternator going bad shouldn’t throw a check engine light. It’s much more common for a bad alternator to illuminate the Battery, ALT, or GEN light in your dashboard.

engine light on your car dashboard.

However, the alternator going bad can sometimes trigger issues with different sensors and cause them to throw error codes. Check out our ultimate guide on can a bad alternator cause false codes and limp mode to find out how a bad alternator can cause issues with sensors.

With that said, it’s not impossible for a bad alternator to cause the check engine light to come on. It could happen in rare cases. A failing alternator can cause all sorts of issues with the electrical system in your car and can wrongly right the check engine light.

Sometimes, you may even find all the lights on your dashboard illuminated due to a bad alternator. Your car will even stop working properly while you’re driving in the middle of the road in these situations.

When you have the CEL turned on due to a bad alternator, you should check your car for error codes with an OBD2 scanner. The error code P0562 points to a bad alternator. If you see that, you need to replace your alternator to get rid of the check engine light.

What Else Causes A Check Engine Light

While it’s possible for an alternator to cause the check engine light in a vehicle, it’s far from being the main reason behind it. There are many other issues that are much more likely to be the ones that are causing the CEL to come on. Here are the most common ones:

Note: You can also read our ultimate guide on can a bad alternator cause rough idle.

1. Gas Cap

The most common issue that throws a check engine light is a gas cap that has not been tightened properly. When you tighten the gas cap all the way, it seals the fuel system and makes sure that the fuel doesn’t escape.

car gas cap

If you don’t screw the gas cap all the way, the vacuum is no longer there and you’ll have fuel escaping from your car. The fuel that could have been used to run your car won’t be utilized properly.

This issue alone is enough to trigger the CEL. Luckily, it’s also one of the easiest issues to fix. Just make sure you tighten your gas cap all the way until you hear it make a clicking noise.

If your gas cap was loose before, doing this thing will get rid of the check engine light after a while. If you have a broken gas cap, you’ll have to replace it.

2. Catalytic Converter

Anything wrong with the emissions equipment in your car can lead to the check engine light coming on. One of the most important and expensive components of emissions in a car is a catalytic converter.

car catalytic converter

The catalytic converter reduces harmful emissions in your car by converting carbon monoxide into carbon dioxide. It also improves fuel efficiency and helps improve performance.

Your car will no longer pass the emission tests if the catalytic converter doesn’t work properly. That can trigger the check engine light. If your CEL is accompanied by a smell of rotten eggs, there’s a strong chance that you have a bad catalytic converter.

Try taking out the catalytic converter and cleaning it first and see if that solves the issue. Keep in mind that there’s potentially something else wrong with the emissions system in your car that caused the catalytic converter to go bad. 

Figure it what caused the catalytic converter and have it fixed. It’s important to do it before you replace the catalytic converter. That’s because the catalytic converter is expensive and you don’t want to replace it again.

3. Spark Plugs

Fouled or worn-out spark plugs are another common reason behind getting the CEL turned on. The spark plugs need to fire at the right time to ignite the mixture of air and fuel in an engine.

car spark plugs

When it doesn’t do that, the engine misfires. It increases the hydrocarbon emissions from your car and also results in a weaker performance. If you’ve driven your car for more than 10,000 miles since the last time you replaced your spark plugs, you should check them out.

Pull out the spark plugs in your vehicle and inspect them. If they are damaged, replace the entire set of spark plugs. When the engine starts to fire correctly, the check engine light will go away soon.

4. Mass Airflow Sensor

The MAF sensor determines the amount of air entering your engine and sends that data to the ECU. This data is used to calculate the right amount of fuel required to end up with an optimum mixture of air and fuel.

mass airflow sensor

When the MAF sensor fails to do its job properly, it sends the wrong data to the ECU regarding how much air has actually entered the engine. But the ECU uses that to send the fuel via the fuel injectors.

The air-fuel mixture gets thrown off and it leads to an engine misfire in many cases. It can cause the CEL to come on. Sometimes, the MAF sensor can get dirty due to the build-up of oil or other elements.

You can try cleaning it first and see if that solves the problem. If it doesn’t work, you’ll have to replace it with a new one. Thankfully, MAF sensors are pretty cheap and easy to replace.

5. Oxygen Sensor

The oxygen sensors in your car also measure the amount of unburnt oxygen that has gotten into the exhaust. It sends this data to the ECU and helps the process of getting the unburnt oxygen back into the combustion chamber where it gets burned.

car oxygen sensor

Too little or too much unburned oxygen can damage the other components in your engine. So, a faulty oxygen sensor can trigger the check engine light. Get it replaced to solve the issue. The check engine light will go away on its own if you keep driving your vehicle after a while.

If you want it to go away immediately, turn the engine on and off three times back to back. If that doesn’t work, disconnect the positive terminal of the battery, leave it for 15 minutes, and connect it again. The CEL will go away and won’t come back unless there are other issues in your car.

How To Tell If You Have A Bad Alternator

It’s not common for an alternator to go bad all of a sudden. You’ll most likely get several warning signs before an alternator actually fails. If you see any of the common symptoms of a bad alternator along with the check engine light in your car, you can isolate the problem to the alternator with more certainty.

car alternator

Here are the signs that will help you identify whether you have an alternator that could be faulty:

  • Flickering lights on your dashboard that get either too dim or too bright.
  • Weird noises coming from the serpentine belt.
  • A dead battery as the alternator isn’t able to charge it.
  • Electrical issues in your car.
  • The engine is stalling and you’re having difficulty starting it.

If you notice a few of these signs together, it’s safe to assume that you have a bad alternator. Getting an OBD2 scanner that reveals the P0562 code also supports the diagnosis of a bad alternator.

As a final test, you can get your alternator checked with a multimeter. The output range of the alternator should be between 13V and 14.5V when the car is on. If the readings are out of this range, then you can conclude that you have a bad alternator. You can replace it to solve the problem.

How Serious Is A Check Engine Light

Generally speaking, a check engine light is a pretty serious issue on its own. It encourages the driver to have their engines checked as there is certainly something wrong with it.

car check engine light

As most drivers are used to ignoring the check engine light until something catastrophic happens, the check engine light lights up in different ways to indicate the seriousness of the issue. Here’s what you need to know about how you should deal with a check engine light depending on its type:

1. CEL Comes On Only In Certain Driving Conditions

This type of check engine light warning is generally the lightest one. For example, if the light appears when you’re driving in the city but goes away when you’re on the freeway, it can be isolated to the driving conditions of the city. The CEL may also flicker in this condition.

If you notice any performance issues with the car when the CEL turns on, you should drive to a repair shop immediately. However, if there are no noticeable differences, you can take your car home.

Even if you decide to drive it home, it’s recommended that you have it checked out soon. There’s always the risk of the car failing to start or dying on the road if you don’t address the issue while there is still time.

2. CEL Comes On & Stays On

Another type of issue you’ll be facing is that the CEL will come on and stay on but not in certain driving conditions like the last time. It will stay on all the time as long as you’re driving your car.

If there are no performance issues, it’s likely that the issue is with your emission control system and that’s what triggered the check engine light. Getting it fixed should get rid of the light.

But it’s a more serious issue if the CEL stays on and there are performance issues at the same time. This type of warning usually means that a vital engine component has gone bad and that’s taking a toll on the entire engine.

If you don’t address this issue soon, you are risking total engine failure. It’s a bad idea to keep driving your vehicle in this condition. Your ideal course of action should be to pull over to a safe spot on the road and get your vehicle towed to a close auto repair shop.

This type of check engine light is the most serious one. If your check engine light comes on and blinks in a steady pattern, your car is in trouble. It’s not like the flickering engine light where it flashes every second.

For example, the pattern here is the light being steady at normal speed and flashing when you press the acceleration. The exact pattern may vary in your case.

The color of the check engine light may also be changed to red or orange instead of the normal yellow color to indicate a more severe issue. Either way, you need to get your car checked right away if you’re seeing this check engine light in the dash of your car.


Can low levels of oil trigger the check engine light?

Running low on oil is a serious issue but it’s not likely to trigger the CEL. It’ll most likely trigger the oil light in your dash. However, low oil pressure can make the check engine light come on.

Is it safe to drive with the check engine light illuminated?

The simple answer is no. Your first priority should always be to get the car checked out as soon as you can whenever you see the CEL.

Will the check engine light go away on its own?

If you’ve fixed the issue that made the CEL come on, it can turn off by itself after driving for a while. But sometimes, you’d have to manually reset it either by disconnecting the battery or using an OBD2 scanner.

Can a bad battery cause a check engine light to come on?

The chances of a bad battery throwing a check engine light are similar to that of the alternator doing it. It’s rare but can happen on a few occasions as issues with the battery can also cause problems in the electrical system.


Can a bad alternator cause check engine light? By now, you should know that it’s a rare occurrence but not impossible. When it happens, all you have to do is to replace the alternator and the problem will disappear.

However, the check engine light can also be caused by the other issues we mentioned in this guide. Make sure you diagnose and rule them out as well. Comment below and let us know what triggered the CEL in your case.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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