6 Symptoms of Faulty Glow Plugs

6 Symptoms of Faulty Glow Plugs

Do you drive a diesel car or truck? Glow plugs preheat your engine so it starts easier in cold weather. As you can imagine, they’re super important, but they don’t last forever. Let’s take a closer look at the difference between glow plugs and spark plugs, the symptoms of a failed glow plug, and how much it costs to replace them.

What are glow plugs? Glow plugs generate heat to warm the engine’s cylinders and ignite the fuel. Without them, a diesel engine would not start.

Glow plugs not only heat and ignite a diesel engine, but also keep the engine running smoothly. Most vehicles have glow plugs installed in the combustion chamber to efficiently provide heat to a diesel engine.

Under ideal weather conditions, a defective glow plug will make it difficult to generate enough heat to warm the cylinders and ignite the fuel. In icy weather, a defective glow plug will not function at all.

Symptoms of a failed glow plug
If your diesel vehicle has at least one of the following symptoms, it is likely that one or more glow plugs are defective.

1) Difficulty starting the vehicle

One of the most common symptoms of a defective glow plug is that the vehicle is difficult to start. This is especially true in cold weather.

Glow plugs are responsible for heating the combustion chamber to the optimum temperature for efficient fuel ignition. If one or more glow plugs are not functioning properly, they may not be able to generate enough heat to warm the cylinders and effectively ignite the fuel.

This can result in difficult starting and multiple attempts to start the engine. In rare cases, especially if the glow plugs reach the end of their life and temperatures drop below freezing, the vehicle may not start at all.

2) Poor Acceleration

Even if you are able to start your diesel engine with bad glow plugs, you may notice a decrease in overall performance. This is especially true if your vehicle does not respond with normal power or acceleration when you step on the accelerator. The engine may feel slow and have difficulty reaching high speeds.

Poor acceleration can be caused by a variety of engine problems, but if you notice this symptom along with other signs of bad glow plugs, your glow plugs may be the culprit.

3) Misfire

Exhaust misfires can cause a lot of problems for your vehicle. This occurs when the fuel in the cylinders does not ignite properly. Since glow plugs play a vital role in igniting the fuel, we can assume that misfires in diesel engines may have something to do with glow plugs.

  • Misfires are also a common sign of bad glow plugs and can cause a variety of problems for your vehicle.
  • Misfires occur when the fuel in the cylinders does not ignite properly and unburned fuel is expelled through the exhaust.
  • Misfires can cause rough idling, slow acceleration, and even engine stalling. Simply ignoring a misfire can lead to increased emissions, reduced fuel efficiency, and damage to other engine components.

4) Thick Exhaust Smoke

Several factors can cause thick gray or black exhaust smoke. If there is a problem with the combustion process, it could be that your glow plugs are the culprit.

Black smoke during acceleration is more common in diesel engines, but if this symptom also occurs in other engines on this list, it could be due to faulty glow plugs.

If there is an abnormal amount of thick grey or black smoke coming from the exhaust, this could be a sign of a faulty glow plug. There are several factors that could cause abnormal exhaust smoke, but if there is a problem with the combustion process, it could be that your glow plugs are the culprit.

If the plugs do not heat the combustion chamber sufficiently, the fuel may not burn completely and unburned fuel may be expelled through the exhaust system. This can result in dark, thick smoke, especially under hard acceleration.

5) Check the engine light

Modern diesel vehicles (1996 and newer) are equipped with sophisticated engine management systems that monitor a variety of components, including the glow plugs. If one or more glow plugs are not functioning, the check engine light on the dashboard may come on.

A scan with an OBD2 scanner will show glow plug-related trouble codes, such as P0380, which stands for “Glow Plug/Heater Circuit Failure ‘A'”.

Other glow plug related diagnostic trouble codes include P0381, P0382, P0383, P0384, P0670, P0671, P0672, P0673, P0674, P0675, P0676, P0677, P0678, P0681 and P84.

6) Reduced Fuel Consumption

As mentioned above, defective glow plugs can cause incomplete combustion, meaning not all of the fuel is burned efficiently. This can significantly reduce your vehicle’s fuel consumption.

If you find yourself having to refill your tank more often than usual and experiencing other symptoms of bad glow plugs, the cause is probably your glow plugs. Make sure you replace your glow plugs. If you don’t, you’ll literally be burning money (fuel).

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