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What Does a Diesel Engine Pre-Glow Warning Mean?

If your car runs on diesel, you may have noticed an unfamiliar dashboard light that looks like a coil come on in cold temperatures.

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If you see a diesel engine pre-glow warning light come on steady at startup, it simply means that your engine is in the process of warming up and you will be able to start your car or truck momentarily. If the light is flashing, it means that there’s an issue with the system that warms up the engine, such as a worn-out glow plug.

To help you better understand the system that this little light speaks for, Automotive Training Center popped under the hood to take a look.

Light is On Steady: Your Engine is Too Cold to Start

The Cold Prevents Diesel Engines From StartingUnlike gas engines which require a spark plug to kick off the combustion process, diesel engines need pressurized hot air to set off the ignition cycle.

During PA’s chilliest months, the temperature inside the engine is below what it needs to be in order to get the engine going. Diesel engines are equipped with heating elements called glow plugs that sense the engine temperature and are turned on when it’s too cold to start.

Luckily, glow plugs are able to warm the engine fast, usually in under 30 seconds. Once the right temperature is reached, the pre-glow warning will fade away and you will be able to turn the key fully and start your vehicle’s engine.

Light is Blinking: You May Have a Faulty Glow Plug or Timer

Dashboard LightIf you’re unable to start the engine and see the coil symbol blinking intermittently on your dashboard, this indicates a problem with the system that you’ll want to get taken care of by an experienced diesel technician. What could it be?

A blinking pre-glow warning light is often due to glow plugs that have lost their heating ability and can’t get the engine to the right temperature to start. Another common issue with the pre-heat process may be a problem with the timer that tells the glow plugs how long to stay on—if the timer never tells the plugs to stop heating, they can just as easily wear out and require replacement.

If you have a blinking diesel engine pre-glow warning light, your car will file away a diagnostic trouble code or DTC for the issue in its onboard diagnostic system. Using a scan tool, a trained automotive diesel technician will be able to receive the code and know what to do next in order to remedy the problem.

Learn More about How Diesel Engines Work

Diesel engines are fascinating feats of engineering. With incredible strength, durability, and fuel efficiency, diesel powers everything from sporty hatchbacks to 18-wheeler shipping trucks.

Feel free to reach out to our staff at our Warminster or Exton campus with any questions!

If you’re interested in learning more about diesel engines, you might have some questions you’re itching to get answered. Check out our free eBook, Everything You Wanted to Know about Diesel (But Were Too Afraid to Ask) to get some more background on these exciting machines and everything they’re capable of.

For program disclosure information, please go to www.autotraining.edu/consumer-information.

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