Skip the auto shop - Our mechanics make house calls

Symptoms of Bad or Failing Glow Plugs

glow plugs

Glow plugs are an engine management component that is found on vehicles equipped with diesel engines. Their purpose is to preheat, and help warm up the engine’s cylinders so that diesel combustion can occur more easily. They play an especially important part in warming the vehicle’s cylinders during cold starts, where starting the engine is most difficult. Glow plugs use an electrode which will warm up and glow orange when current is applied. When the glow plugs have an issue, they can usually cause problems with the driveability of the vehicle. Usually bad or failing glow plugs will produce a few symptoms that can alert the driver of a potential issue.

1. Engine misfires or decrease in power and acceleration

Engine misfires are one of the first symptoms of an issue with the vehicle’s glow plugs. If the glow plugs malfunction they will not provide the additional heat that aids in diesel combustion, which may cause the engine to experience misfires. The misfires may cause a loss in power, acceleration, and even fuel efficiency.

2. Hard starting

Another symptom of an issue with the vehicle’s glow plugs is hard starting. Unlike gasoline engines, which use a spark to ignite the fuel mixture, diesel engines rely solely on cylinder pressures to ignite the diesel fuel mixture. If the glow plugs fail, the engine will have to overcome additional pressure in order to ignite the mixture, which may result in hard starting.

3. Black smoke from the exhaust

Another symptom of an issue with the glow plugs is black smoke from the exhaust. Faulty glow plugs may disturb the sensitive diesel combustion process, which may cause the engine to produce black smoke from the tailpipe. Black smoke can also be caused by a wide variety of other issues, so having the engine properly diagnosed is highly recommended.

Glow plugs are found on virtually all diesel engines, and play an important role in starting and operating the engine. If your vehicle is displaying any of the symptoms above, or you suspect that your glow plugs may be having an issue, have the vehicle inspected by a professional technician, such as one from yourMechanic, to determine if the glow plugs need to be replaced.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Post a question and get free advice from our certified mechanics.

ASK A QUESTION

More related articles

How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...
P2159 OBD-II Trouble Code: Vehicle Speed Sensor B Range/Performance
Diagnostic Trouble Code (DTC): P2159 P2159 code definition Vehicle Speed Sensor B Range/Performance Related Trouble Codes: P2158: Vehicle Speed Sensor B P2160: Vehicle Speed Sensor B Circuit Low P2161:...
P0291OBD-II Trouble Code: Cylinder 11 Injector Circuit Low
P0291 code definition When your vehicle’s PCM registers the P0291 code, it means that a voltage reading came from the fuel injector circuit – for cylinder number 11’s fuel injector –...


Related questions

Q: How Do Spark Plugs Work in an Engine?

Spark plugs are used to ignite the air/fuel mixture in the combustion chambers of every internal combustion engine. To accomplish this, spark plugs have two electrodes between which a high voltage spark will jump. One electrode is located in the...

Q: My truck won't start on the key but will start straight up on a jump start I have changed the glow plugs and the deisel pipes

Hello. If your car will not start on its own, but will with a jump start, then the first thing I would check is the battery. If the battery is old or worn it may no longer have enough cranking...

Q: Glow Plug System light comes on sometimes and engine has a lack of power when the light is on.

Hi there. Check the glow plug relay and see if its plugged in. Check the circuits to the glow plugs and see if there is power to them when the key is turned on. The circuit to the glow plugs...