If you drive a Mercedes-Benz with a diesel engine, it uses glow plugs. This is opposed to spark plugs used in gasoline engines, which are typically more well known. The purpose of such plugs is to ignite the air/fuel mixture in the cylinders of the vehicle. However, glow plugs serve a primary purpose in starting the vehicle (ignition), while spark plugs run constantly during driving, continually firing in order with the engine’s configuration. Although glow plugs have their differences from spark plugs, trouble with either system can lead to similar problems.

Just like gasoline engines must have their spark plugs in working order, so too must diesel engines with their glow plugs. Let’s go over some of the signs your Mercedes has one or more bad glow plugs and how it can be fixed.

Signs You Have a Bad Glow Plug in Your Mercedes

  • Check engine light: The check engine light can signal a wide variety of issues, including bad glow plugs. However, it is best to have the code scanned as soon as possible to find out the exact problem your Mercedes has pinpointed.
  • Hard to start: Your Mercedes might become hard to start. This is especially true in colder temperatures, because diesel engines often require heat from the glow plugs to start effectively when the outside air is cold. You might not notice this during the summer, when the ambient air is already very warm, because the temperature might be high enough to start your engine without the help of the glow plugs.
  • Misfire: An engine misfire means the air/fuel mixture is not detonating during combustion properly or at all. For example, one or more cylinders in your Mercedes might not fire, meaning the car will not be running completely. This can be caused by factors external to glow plugs, of course, and misfires are a serious concern that ought to be inspected immediately, but the plug cannot be ruled out as a possible reason for your suddenly poor running engine.
  • Rough idle: In line with poor running conditions, your engine might seem to idle more roughly than it used to. You might notice it sounds off, as if it is sputtering or stuttering. You might even hear it “miss”, as if the engine’s pulse skips a beat, signaling misfiring. Rough idling and misfiring are two different events, but often go hand in hand.
  • Reduced fuel economy: If your Mercedes just isn’t getting the same miles per gallon as before, the glow plugs might be to blame. This is because sometimes diesel fuel contains additives to affect the freezing point of the fuel. This is often done during colder months/in colder climates. In turn, this lends even greater importance to your glow plugs in providing sufficient heat for ignition.
  • Smoke: White or black smoke from the exhaust can both signal bad glow plugs. White smoke usually indicates one or more glow plugs is worn or damaged, while black smoke indicates a rich running condition. To run rich means there is too much fuel and too little air in the combustion chamber, leading to the dark smoke (unburned fuel) emanating from the exhaust. Although this too, like many of the other signs, can be caused by problems with other systems, glow plugs cannot be ruled out as their malfunctioning can cause problems with the combustion process as a whole.

As can be seen above, there are several signs warning you that your glow plugs might be bad. These signs are all pertinent warnings and should be addressed by a reputable mechanic as soon as possible to prevent further damage and get you and your Mercedes safely back on the road.

Mercedes Glow Plugs

Escondido German Auto for your Mercedes Glow Plug Service

Escondido German Auto is a leader in services for European vehicles including Mercedes-Benz. We employ ASE certified technicians who use manufacturer approved parts. We understand how hard it can be to diagnose your car’s issue, and we pride ourselves on helping you do so with honesty and integrity.

You can find us at 554 E. Grand Ave. in Escondido, CA 92027. Customers also come from surrounding regions such as Rancho Bernardo and Valley Center, CA. To schedule an appointment, call us at (760) 741-3905 or use our website. We look forward to earning your patronage.

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