Symptoms of a bad glow plug

Symptoms Of a Bad Glow Plug

If you operate a diesel vehicle, you should be aware of the symptoms of a bad glow plug and how they affect the longevity and functionality of your car. In order to warm up the engine’s cylinder and ignite the fuel, a glow plug produces heat. Your diesel engine won’t start without it. Glow plugs not only warm and start diesel engines, but also keep your engine running smoothly.

The glow plug is typically put inside the combustion chamber of cars so that it can effectively transfer heat to the diesel engine. A malfunctioning glow plug will find it difficult to produce enough heat to preheat a cylinder and ignite the fuel under perfect weather circumstances. A broken glow plug won’t function at all in subzero temperatures.

Symptoms of a bad glow plug

Well, in this article, we’ll go over the most common symptoms of a bad glow plug. That said, we’ll look at why glow plug goes bad, whether you can drive, how often should you replace the plug, and the cost of replacing it. So, without wasting any more time, let’s get down to it!


Symptoms Of a Bad Glow Plug

Here are the most common signs and symptoms of a bad glow plug:

  • Having trouble starting the car
  • Check Engine Light
  • Misfiring
  • Sluggish acceleration
  • Dark Gray or Black Exhaust Smoke

Having trouble starting the car

With damaged glow plugs, a diesel engine cannot be started. Glow plug malfunctions prevent enough heat from being produced to preheat the cylinder and ignite the fuel. It can take numerous attempts to start the car if heat cannot be produced quickly enough. The car won’t start at all if the glow plugs are almost dead and it’s chilly outdoors.

Check Engine Light

A defective glow plug may cause the check engine light to come on, and an OBD2 scanner will display an error code that has to do with glow plugs, such as P0380, which stands for “Glow Plug/Heater Circuit ‘A’ Malfunction.” P0381, P0382, P0383, P0384, P0670, P0671, P0672, P0673, P0674, P0675, P0676, P0677, P0678, P0679, P0680, P0681, P0682, P0683, and P0684 are additional glow plug-related diagnostic issue codes.


A backfiring exhaust can damage your car in a number of ways. It happens when the fuel inside the cylinder doesn’t ignite properly. You can presume that your glow plugs may be the cause of a misfire in a diesel engine since they are so important in the process of igniting gasoline.

Sluggish acceleration

Even if a damaged glow plug can start a diesel engine, the car won’t run at its best. When you press all the way down on the accelerator without gaining much speed, you’ll notice an early symptom of decreased performance.

Other engine issues can also result in poor acceleration. However, if you also experience any of these additional signs of a damaged glow plug in addition to poor acceleration, your glow plugs are probably to blame.

Dark Gray or Black Exhaust Smoke

The causes of dark gray or black exhaust smoke are numerous. You can experience a glow plug issue if the combustion process is at fault. Dark smoke when accelerating is more typical with diesel engines, but if it also occurs with other symptoms on this list, a malfunctioning glow plug may be to blame.

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Why glow plugs go bad

Diesel glow plug issues can take many different forms. High voltages or extreme heat are the two main causes of glow plug failure. A controller that is beginning to malfunction could be the source of high voltage. Additionally, the glow plug(s) may be receiving electricity continuously if there is bad wiring or a controller issue.

The plugs will burn out before they should because they are not intended to be left on all the time. Additionally, the engine’s timing or gasoline leaking from the injector(s) can result in extreme heat conditions. It goes without saying that running the engine on gasoline will destroy the glow plug tips because of the heat buildup in the pre-chamber.

Can You Drive with a bad glow plug?

Glow plugs will eventually deteriorate and have a detrimental impact on your car’s performance. The car may still start, and you can still operate it, but it won’t run as well as it did when it had sound glow plugs. Starting the car will require several attempts as the glow plugs deteriorate, and accelerating hard will be necessary to reach higher speeds.

The vehicle won’t start at all if you reside in a colder climate since the glow plugs can’t provide enough heat to initiate combustion. Faulty glow plugs won’t just make starting the engine more difficult and force you to drive at lower speeds; they’ll also diminish your car’s fuel efficiency. Additionally, they will make the car’s carbon impact larger. By replacing your plugs as soon as you discover any signs of a defective glow plug, you can avoid these expenses and inconveniences.

How often to replace this plug?

Glow Plug Lifetime: Glow plugs should last up to 100,000 miles before gradually degrading as a result of wear and tear. The good news is that glow plugs are among the least expensive auto parts to replace and have a very long lifespan. So, all we’re just saying is, replace your glow plug as often as every 100,000 miles. This will help you maintain your car’s overall health and performance.

How much does it cost to replace the glow plug?

You should be aware that glow plug replacements are inexpensive if you put off changing your glow plugs due to the price. You may get a replacement glow plug for anywhere between $25 and $50, depending on the brand and quality. If you have the necessary tools, changing the plugs yourself will save you money on labor.

You can pay a mechanic labor fee of $90 to $200 to replace your glow plugs if you want to put convenience over quality. The process could take up to two hours, depending on the layout of your engine and the mechanic’s level of experience. The more labor expenditures you incur, the longer the job will take.

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What problems can glow plugs cause?

In short, delayed starting and complete inability to start are common glow plug issues. When the car does start, there will be loads of white smoke while it heats up, a rough idle, and hesitation. If your four-cylinder engine has one defective glow plug, it will start slightly harder and miss.

Do glow plugs affect acceleration?

Low acceleration when you press firmly on the gas pedal is a frequent issue. When you let off the gas pedal while driving a diesel vehicle, the engine won’t move forward. Misfires in the engine, which are both frequent indicators of worn-out or defective glow plugs, might result in a loss of power.

Will a diesel run with bad glow plugs?

No, driving while using a malfunctioning glow plug is unsafe. Your engine will misfire or run rough as a result of an insufficient fuel ignition caused by an inappropriate combustion chamber temperature.

Are glow plugs just for starting?

Although glow plugs may appear to be trivial, they are an integral part of any vehicle’s diesel system and carry out a number of vital functions. not only during initial ignition but also throughout the entire cycle, which largely occurs in the background without being observed.

How often should you change glow plugs in a diesel engine?

Glow plugs should last up to 100,000 miles before gradually degrading as a result of wear and tear.

Will bad glow plugs throw a code?

When your check engine light illuminates: The emissions of your car will be entirely out of wack if you have a defective glow plug. Your engine computer may undoubtedly activate the check engine light on your dashboard as a result of this circumstance.

How much does it cost to replace diesel glow plugs?

Glow plug replacements typically cost between $238 and $291. While materials are priced between $99 and $114, labor costs are predicted to range between $140 and $176.

Does changing glow plugs make a difference?

Engine performance is fundamentally dependent on glow plugs. When the key is turned, they send out a tiny spark of electricity to keep your engine running. They can cause expensive engine damage if they aren’t inspected during routine maintenance and replaced as they become worn.

Bottom Line

The dashboard’s engine warning light is frequently the first indicator that something is wrong. Vehicles with this light on should be taken as soon as possible to an authorized workshop for an accurate diagnosis and service.

And that is all for this article, in which we discussed the most common symptoms of a bad glow plug. Even so, we took a closer at why glow plug goes bad, if you can drive, how often you should replace the plug, and the cost of replacing it.

Hope it was helpful. If so, kindly share it with others. Thanks for reading; see you around!


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