Symptoms of a Bad Diesel Glow Plugs

November 11, 2019MechVibesblog

Diesel cars won’t start when cold – could be glow plugs? Want to know the major symptoms of a bad diesel glow plugs? Diesel glow plug is an electrically heated thin metal that helps diesel cars to start at cold temperatures. It provides enough heat for the fuel and air mixture in the combustion chamber.

Diesel glow plus works only at cold temperatures/during winter seasons. Diesel engine uses very high compression of the mixture to produce the heat required to ignite it.

As glow plugs play a major role in starting of a vehicle, but a bad glow plug can cause your vehicle engine performance.


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  • Black Exhaust Smoke
  • Hard Starting
  • Engine Misfire
  • MIL stays on.

Black Exhaust Smoke

Faulty glow plus hardly makes various sensors involved in the diesel combustion process respond. It sends a bad reading signals.

Also, this disturbs the sensitive combustion process which as a results produces black smoke released from the exhaust tail pipe.

Hard Starting

One major symptom of a faulty diesel glow plug is hard starting. Diesel cars are mainly built where additional pressure is required in order to ignite air-fuel mixtures, glow plugs are needed to perform such functions.

If diesel glow plug fails, this results in hard starting.

Engine Misfire

A faulty diesel glow plug can cause vehicle engine to misfire. This causes poor performance, decrease in fuel efficiency and loss of power.

Malfunction Indicator Light(MIL) Stays On

When your diesel glow plug is faulty, additional symptom to factor is the MIL , you find out that your MIL stays on dashboard. MIL also known as check engine light.


Almost all diesel cars have glow plugs and is essential for a complete combustion at cold temperatures.

Besides, what do you think we should have add-up which could be helpful, let us know in the comment box.

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