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Glow Plug Not Working? (3 Ways To Tell)

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Glow Plug Not Working? (3 Ways To Tell)

You look at your dashboard, and you see the dreaded orange light indicating that your glow plug isn’t working.
If you’re new to the world of diesel, you might wonder what the heck this light is- or even what a glow plug is.
You might even consider leaving it on for a little bit. Hey, if our younger selves can play Russian Roulette with an empty gas tank light, the glow plug light can flash for a while.
No biggie. Right? Well, no. Not exactly. Defective glow plugs shouldn’t be ignored; pretty quickly, they do affect a vehicles driveability. A glow plug is essentially a heating element that heats the air and fuel in the cylinders of an engine, causing fuel combustion. And since that’s how the engine starts, keeping your glow plugs working is a good idea.
In the pre-chamber or combustion changer in your engines cylinder there is one single glow plug. Depending on whether you have pre chambered engine or a direct-injection engine, the role of a glow plug doesn’t differ. Glow plugs are a huge factor in how easily your car starts in the winter months, when cylinders need more of a boost to get going.
Did you know? The glow plug system in your diesel engine heavily affects the starting process of an engine. The components of a glow plug system- glow plug control modules, glow plug relays and glow plug combustion sensors- can play a huge role in decreasing emissions. Win for the environment!

Symptoms of a Glow Plug That Isn’t Working

Defective glow plugs aren’t usually a hidden problem for drivers- there a few symptoms that will give it away. Superior Diesel shares three main things that indicate a likely problem with your diesel vehicles glow plugs.

Engine Misfires & Loss of Power

Perhaps the biggest indicator of failing glow plugs, engine misfires typically occur because the glow plugs are not encouraging enough combustion in the engine. Frequent engine misfires result in a loss of power and acceleration, and will have a negative effect on the fuel efficiency of your tank.

Your Vehicle is Hard to Start

Unlike their gasoline counterparts, diesel engines rely on cylinder pressures to get the engine going. Without working glow plugs, your engine will have to work overtime under additional pressure in order to get the engine to work- and this will likey be a hard start for your engine.
Exhaust Smoke: There are actually many reasons for excessive black exhaust smoke, so this typically isn’t the strongest indicator of failing glow plugs. However, in conjunction with other issues, it can help steer you to the root of the problem (if the plugs really are the issue.) When your glow plugs aren’t working that well, they may disrupt the combustion process in your engine. Since this process is sensitive, faulty glow plugs can taint the fuel in your engine and produce an excess of black exhaust smoke.

What To Do If Your Glow Plugs Aren’t Working

We really don’t recommend replacing glow plugs yourself. The process is finicky, to say the least and can do more damage than intended if done incorrectly.
If you feel mechanically inclined to do so, however, you can look at the following steps to try and fix broken glow plugs:

Disconnect the battery cable

You should always disconnect the battery cable before working on the electrical system in your vehicle, but we do see people forget. Locate the negative battery cable and disconnect.

Remove the valve cover

Only applicable if your glow plugs are located under the valve covers. If so, remove it by unscrewing all screws around the perimeter of the cover.
PSA: Great time to see if the valve cover gaskets need replacing!

Find the glow plugs

Look at the head of the cylinder, and your glow plugs will be screwed into there. Keep an eye out for the wire, as this is the plugs power supply.

Stop the power supply to the glow plugs

Disconnect the power supply by removing the wire from the glow plug. There will be a connection device to do this; unfasten the terminal and put the wires to the side.

Remove the glow plug

To remove the plug, use a rachet and socket. Turn the ratchet left over the plug – counterclockwise- and keep in mind, this may require a deep socket.
PSA: Badly damaged glow plugs may break down while in the engine; be sure to remove all the broken pieces.

Install new glow plugs

After cleaning the surrounding area, hand tighten the new glow plugs into position. Again, with your rachet and socket, work the glow plugs into place- but, not too tight! Too tight of an installation will damage the plug.

Reattach power supply

Give the glow plugs the power they need by reattaching the wires outlined in step 4 above. Be sure to reattach them in the exact same place and method you removed them during step 4.

Replace the valve covers

Put those babies back on if you had to take them off during step 2. Use the ratchet to tighten the screws removed with the valve box after you swapped out the gasket.

Connect the negative battery cable

Reconnect the battery to the negative battery cable. At this stage, you can test the glow plugs using a scan tool.

Regardless, a Good Diesel Repair Shop Has You Covered

Unless you have experience, working on particular issues- especially with a diesel engine- can more damage than good. Diesel vehicles are sensitive, especially components such as glow plugs. Keep your ride on the road, driving perfectly, and save the repairs for your local diesel repair shop.