Can You Drive With a Lit Glow Plug Light? Plus Related FAQs

The glow plug light on your dashboard might light up out of the blue while you’re driving. This means there’s something wrong with your vehicle’s glow plugs that requires your immediate attention. Fortunately, it’s no reason to panic.

You’ll still be able to drive your vehicle, but you need to be extra careful. Also, your next destination must be the closest auto repair shop so a professional can diagnose your engine.

What Does It Mean When the Glow Plug Light is Lit?

If the glow plug warning light on your vehicle’s dashboard suddenly lights up, it means there’s something wrong with the glow plugs in the engine.

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Pro Tip: The glow plug light is more of an indicator than a warning light. If it comes on while driving, something is wrong with the module or the wiring circuits.

An illuminated glow plug indicator tells you there’s something related to the glow plug system that requires your attention: usually, a damaged, malfunctioning part. Newer diesels are wired to measure the resistance and/or current draw on each separate glow plug and can set codes accordingly.

Can You Drive With a Lit Glow Plug Light?

Yes, you can as long as the problem that triggered the glow plug light isn’t too severe. To be on the safe side, it’s best to avoid driving vehicles with malfunctioning parts.

It should be safe to drive around the city where you don’t need to go at high speeds and help is readily available in case your vehicle does break down.

On the other hand, you should refrain from driving long distances or taking the highway if you have a lit glow plug light.

Your vehicle might enter a protective state called “safety mode” by itself to minimize potential damage when the glow plug light activates. In this state, the performance of the engine declines significantly. Your vehicle will slow down, turning into a safety hazard on busy, fast roads like highways.

What Should You Do If the Glow Plug Light is Lit?

If your vehicle’s glow plug light activates, you should do one of two things: replace the glow plugs or get them repaired.

The first thing you should do is pull over and inspect your vehicle’s engine. Glow plug lights heat up to kickstart the engine, but they turn off after doing their job.

If your engine is hot, it might be a sign that the glow plugs haven’t been deactivated and are still heating up your engine.

In this case, drive your vehicle to an auto repair shop or have it towed.

Purpose of Glow Plugs

Let’s talk about why glow plugs and manifold heaters are necessary. Diesel engines don’t have spark plugs. Rapidly compressing air in a closed space increases its temperature 2 degrees Fahrenheit. With each compression stroke of a diesel piston, the air that is drawn in through the intake valves is trapped and compressed to between 400 and 500 pounds per square inch.

What this means is that even before the fuel is injected, the air squeezed between the rising piston and the cylinder head above it has reached between 800 and 1,000 degrees Fahrenheit. Since the flash point of diesel is between 125 and 180 degrees Fahrenheit, you can see how ignition takes place on a diesel as soon as fuel is injected into this superheated compressed air.

The challenge is that when the engine is cold, the heat generated by the compression is absorbed by the piston and the head. Without glow plugs or a manifold heater, a cold diesel engine won’t easily start.

Glow plugs get really hot really fast. The current that heats them is delivered by a heavy duty relay or set of transistors controlled by an electronic module. The module also illuminates the glow plug indicator light that lets the driver know when the glow plugs have produced enough heat for the engine to start when the engine is cold.

What Triggers the Glow Plug Dashboard Light?

Besides knowing what to do if your glow plug dashboard light comes on, it’s also important to get the lowdown on the problems that could trigger the warning light in the first place.

Faulty Engine Control Module

The engine control module controls the allocation of power to the glow plugs. If this module gets damaged, it might affect your glow plugs’ performance.

Fortunately, replacing an engine control module is something you can do at home, provided you have the necessary tools and a replacement module available. If you’re not confident with DIY-ing the repairs, you could always bring your vehicle to an auto repair shop.

Problems With The Wires

The glow plugs of your vehicle are connected to the engine’s electrical system with a series of wires. If these wires get damaged, whether due to natural wear and tear or an accident, they can cause the glow plug warning light to activate.

Dealing with bad wiring is tricky, and more often than not, you’ll need to replace the connectors entirely. You can DIY it at home or let a professional do it at an auto repair shop.

Damaged Glow Plugs

Unfortunately, glow plugs are subject to wear and tear just like other vehicle parts. When a glow plug wears out, your vehicle’s smart computer will alert you by turning on the glow plug light.

As always, the best way to deal with this problem is to replace your glow plugs entirely, but it’s also possible to bring your vehicle to a professional for repairs.

More often than not, bad glow plugs lead to serious problems like engine misfires. However, keep in mind that bad glow plugs aren’t the only cause of engine misfires, so a proper diagnosis is a must.

Busted Glow Plug Relay

Much like the engine control module, relays direct power to your vehicle’s glow plugs. These plugs heat up and help start your vehicle’s engine.

You can usually tell if there’s a problem with the glow plug relay if your vehicle has rough starts. The best way to deal with a problem like this is to replace the relays entirely, however, there’s always the possibility that they’re just dirty. You can try cleaning your vehicle’s glow plug relay contacts and see if that deactivates the glow plug light.

What Does A Flashing Glow Plug Light Mean?

It’s one thing to have a glow plug light that stays on, but if it starts flashing, that’s a different problem entirely. If the glow plug light flashes, it means your vehicle has detected a critical problem with the glow plugs in the engine.

Failing to address the problem can potentially lead to serious, irreversible engine damage alongside problems like higher fuel consumption, increased emissions, and engine misfires.

Get a New Glow Plug Delivered to Your Home

If one or more glow plugs fail, it’s best to stop driving your vehicle until you replace the faulty part. You want to minimize further damage to the engine because of the considerable cost of repairing the system if it develops more issues. Fortunately, CarParts.com can help you get a compatible replacement glow plug for your vehicle.

When shopping for glow plugs at CarParts.com, you don’t need to guess which parts fit. Plug the year, make, model, and engine of your car or truck in our vehicle selector to bring up the most suitable products in our extensive catalog of high-quality parts and accessories. Furthermore, we always source our glow plugs from trusted brands, ensuring you get the best bang for your buck from your replacement part. And if you live in the continental U.S. and place your order by 12 p.m. ET, you can expect your new parts to reach your home in a few business days.

Enjoy effortless shopping for competitively priced, high-grade glow plugs at CarParts.com. Don’t miss out on the best deals on glow plugs, and order what you need today!