Glow Plug Relay Problems: An Ultimate Overview in Details!

What are common problems with glow plug relays? Misfiring engines is one of them, though there are some other problems also faced by the vehicle owners.

A glow plug relay is a component in a vehicle’s engine that helps to heat the engine block and cylinders before starting the engine. The relay is responsible for sending power to the glow plugs, which then heat up and help start the engine. However, the glow plug relay also has a limited lifespan, after that, many defects arise.

In this article, we are going through the glow plug relay problems as well as their possible symptoms and reasons. Let’s begin-

A Brief On Glow Plug Relay Problems

Every diesel engine has a glow plug relay and is responsible for supplying power to the glow plugs. When the engine is turned off, the relay remains energized for a set amount of time. This allows the glow plugs to cool down slowly, preventing them from seizing up. The relay can also be used to activate the glow plugs when the engine is cold.

However, there are several common problems with glow plug relays that can cause these issues. Among them, trouble starting, misfires, and glow plug light illumination is the frequent Mercedes glow plug relay problems.

Not only the Mercedes but the other vehicles also have experienced such glow plug relay issues. However, if you aren’t aware of these, your favorite vehicle’s functionalities can be gradually destroyed.

Again, the Ford Fiesta glow plug relay problems include engine cutting out, hard to start in the morning, and so on.

In this circumstance, we decided to focus on the most common and frequent glow plug problems. At the same time, we have depicted the associated reasons for these relay issues in the following table. Have a look-

Problems You Might FacePossible Reasons
Rough startingGlow plug relay problem
Engine misfireBad glow plugs
Less fuel efficiencyExcess heat in the combustion chamber
Low accelerationIgnition issue
Dark smoke emissionAffected diesel combustion

Now, it’s time to discuss the glow plug relay problems from the root to make yourself aware of them. So that you don’t have to suffer in the long run.

1. Rough Starting

If you have a full-sized SUV or personal vehicle, there is a high chance that it has been having starting problems. It happens for the problematic glow plug relay, especially in the morning. The symptoms are that the diesel engine will not start or it will start but then die soon afterward.

There are a few ways to get rid of this problem. One way is to replace the relay. Another is to clean the contacts on the relay with a wire brush. Finally, you could try spraying some electrical contact cleaner onto the relay contacts.

2. Engine Misfire

You may have experienced engine misfires, especially when the weather is cold. The root cause of this problem is usually a bad glow plug relay. When this relay starts to fail, it can’t send power to the glow plugs, which leads to a misfire. Another cause is the fuel engine failing to get the proper ignition in the cylinder. So far, it is regarded as a common 7.3 Powerstroke glow plug relay problem too.

However, there are a few symptoms of a bad relay. One is that the engine will start up fine, but then start to misfire after a few minutes of driving. Other symptoms of this problem include a rough running engine, loss of power, and an illuminated check engine light. The most common way to get rid of this problem is to replace the glow plug relay.

3. Less Fuel Efficiency

If you’re noticing decreased fuel efficiency in your vehicle, it could be due to a problem with the glow plug relay.

This relay is responsible for sending power to the glow plugs, which helps heat the engine so it can start. When this relay fails, it can cause all sorts of problems, including decreased fuel efficiency and difficulty starting the engine. However, the main reason for less fuel efficiency is the excess heat production in the combustion chamber.

Moreover, there are many ways to increase fuel efficiency in Chevy Tahoe. One way is to change your driving habits. Some other ways are to keep your tires inflated properly, remove unnecessary weight from the car, and use the recommended grade of motor oil.

4. Low Acceleration

If you experience a sudden lack of acceleration while driving your car, there are a few things you can check to try and diagnose the problem. The most common reasons for low acceleration are a clogged air filter, low fuel pressure, or a bad spark plug.

Some symptoms that could indicate a more serious problem include engine hesitation, smoke from the exhaust, and a loss of power.

If you have recently replaced any of these items and are still experiencing low acceleration, it may be time to replace the glow plug relay to get rid of this problem.

5. Dark Smoke Emission

In most cases, dark smoke is caused by too much fuel burning in the engine. This can be due to factors such as damaged glow plug relay issues, dirty air filters, or incorrect spark plug gap size.

Moreover, the common symptoms of dark smoke emission can include reduced fuel economy, poor performance, and excessive wear on engine components. While the issue could be something simple, like an improperly adjusted carburetor, it’s best to have it checked out by a professional to avoid further damage and costly repairs.

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Frequently Asked Questions (FAQs)

What Happens When A Glow Plug Relay Fails?

The relay is responsible for sending power to the glow plugs, which heat the diesel fuel and help it start. When the relay fails, the glow plugs won’t get power and they won’t be able to do their job. This can cause your truck to run roughly, and you may experience an engine misfire.

What Does The Glow Plug Relay Do?

The glow plug relay plays a major part in the automatic transmission system. Generally, these relay switches send continuous on/off signals to the glow plugs, depending on how fast you’re going.

How Long Does A Glow Plug Relay Last?

The average lifespan of a glow plug relay is about 150,000 to 180,000 km. However, this lifespan can be shortened if the engine is used for racing or if it’s of low quality. Additionally, the speed at which the engine runs can also affect how long the relay lasts.


In short, we have summarized the most common glow plug relay problems, their reasons, and their symptoms. Hopefully, now you can easily find out and take the proper steps.

So far, problems with the glow plug relay can be a real headache. If you’re experiencing these issues, be sure to troubleshoot and diagnose the problem as soon as possible. Doing so will help you get your vehicle back on the road in no time.

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