5 signs of a bad diesel glow plug in a car and replacement cost


Posted by: Oluwaseun Solomon

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A bad diesel glow plug is a sure culprit that will not only affect overall performance but also the longevity of a car. Check out these 5 signs to spot one!

Like it or not, you can hardly start a diesel-powered engine successfully without the special component known as the “diesel glow plug”.

Yes, this is due to the fact that this special component generates a required amount of heat to start and also operate the car, so if your diesel truck has been given you some unnecessary “headache” recently – you should pay attention to the points discussed below as the top 5 signs of a bad diesel glow plug in a car and replacement cost.


It is almost impossible to have bad/damaged diesel glow plugs in a car without noticing some decline in performance

1. Top 5 signs of a bad diesel glow plug in a car

Driving a vehicle with a diesel engine during the cold seasons would almost be impossible if the diesel glow plug doesn’t generate the right proportion of heat needed to start up the car.

Also, the cylinder head and cylinder block of the engine needs to absorb a greater part of this heat in order to work. This is more reason why you should be able to know if the diesel glow plug in your car is bad if you pay attention to the signs discussed below;

1.1. Engine becoming difficult to start

There are several factors that can cause a vehicle’s engine to face startup problems; as a matter of fact, we have a whole article dedicated to FAQs about starting and engine smoking problems.

Nonetheless, if you notice that you are facing difficulties starting the engine of your diesel-powered car – there is a high probability that the diesel glow plugs could be the first culprit.

Bad/damaged diesel glow plugs in a car will add more pressure to the ignition process thereby making it difficult for the car’s engine to successfully ignite injected diesel fuel.

If you notice that your diesel engine is becoming really difficult to startup recently, seek an auto expert to help you check the diesel glow plugs.


Bad diesel glow plugs could be the reason why your diesel-powered car is having difficulty starting

1.2. Engine misfires more often than before

This is quite similar to point 1 above. When the diesel glow plug is bad and the ignition process is greatly affected, it is obvious that engine misfires would occur more frequently.

You will probably notice that whenever you try to “fire up” the diesel-powered car that has a bad glow plug – you will get regular hit and miss situations. This is one clear sign that you might need to replace the diesel glow plug as soon as possible.


Frequent engine misfire is one of the clear signs that a car might be having bad diesel glow plugs

1.3. Engine light stays on

This is probably the most obvious sign that should notify you of a bad diesel glow plug in your car.

It is not uncommon to notice that the engine check light would come on to hint that something is wrong under the hood.

In some vehicles, you might need to use a dedicated diagnostic scan tool to detect the actual problem causing the engine light to come on. Also, a common code “P0380” is usually the one defined for Heater circuit/Glow Plug malfunction in most vehicles.


Engine light coming on could also be hinting that the car has bad diesel glow plugs

1.4. Black smoke from exhaust pipes

While there are several causes and solutions to black smoke coming from the exhaust pipe of a car, it could sometimes be a sign that the diesel glow plugs are bad.

Just as we have earlier explained in point 1 and 2 above, thick black smoke coming from the tailpipe could be as a result of the bad glow plugs affecting the internal combustion of the diesel fuel.

And even if the glow plugs aren’t actually the cause of the black smoke you are seeing, it is still very bad for any car to be emitting thick black fumes.

Please have your vehicle checked as soon as you can to detect the actual cause and to prevent unnecessary damages to your car engine.

1.5. Reduced acceleration

This sign could also be as a result of many other factors but if you notice reduced acceleration as well as some of the other signs listed above then, it is most likely the diesel glow plug that has gone bad.

You should already see this coming because it is impossible for any driver to enjoy a smooth ride in a car that is having difficulty starting up and also experiencing engine misfire.

You probably don’t need any special knowledge to notice that your vehicle’s acceleration and overall performance is diminishing when it has bad diesel glow plugs.

Want to learn how to remove diesel glow plugs without fear of snapping them? Watch this short video below;

How To Remove Glow Plugs WITHOUT Snapping Them

>>> Read also: Spark plug functions, problems and effects on car performance

2. Replacement cost for a bad diesel glow plug

It will probably cost you between ₦36,400 to ₦80,500 ($95 - $210) to replace the bad diesel glow plugs in your vehicle with brand-new ones. Now, before you get discouraged by this amount; please note that it is just a rough estimate made from shopping online. When planning to replace bad diesel glow plugs, you should keep these 3 important things in mind;

  • Individual plugs actually only cost around ₦5,800 to ₦19,200 ($15 - $50) while mechanics might charge you around ₦30,700 to ₦61,300 ($80 - $160) for their labour. So, in total, expect to spend around ₦36,400 to ₦80,500 ($95 - $210) for the replacement.
  • Each Cylinder in the car engine has a dedicated glow plug which means that a pickup truck with V8 diesel engine needs 8 plugs. This is due to the fact that it is often recommended not to just replace one bad plug but rather all the glow plugs in your engine at once. This is quite similar to replacing bad spark plugs – if one is bad today, there is a high probability that the others could follow suit tomorrow.
  • You should be able to get a lesser/better price from your local mechanic and auto repair shops for these plugs and replacement but the model and brand of your vehicle will still play a huge role in the overall price and charges.


It is often recommended to not just replace one bad diesel glow plug but rather all at once to ensure a proper Fix


Even if you are a new car owner, the above points should be clear enough for you to understand the top 5 signs of a bad diesel glow plug in a car and possible replacement cost. Always pay attention to your car because most of the time, it will give you signs when something goes wrong.

You know Naijauto.com always brings you the best car tips and advice on how to buy and sell cars as well as how to maintain your car the best way. Stay tuned with us to get the latest updates on the auto industry news and cars for sale in Nigeria!

Oluwaseun Solomon

Oluwaseun Solomon

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Oluwaseun Solomon is a prolific and diligent automobile writer at Naijauto.com. He's also an experienced digital marketer and a creative multimedia developer that specializes in video editing. He currently contributes informative and easy to read articles on topics covering transportation, traffic updates, auto industry updates, and different car reviews.
When Solomon is not writing, you will either find him composing music, editing videos or simply enjoying YouTube "TEDx Talk" videos with a chilled drink :)

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