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How to test glow plugs with a multimeter

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If your car is having trouble starting in cold weather, one potential issue could be the glow plugs. These plugs help to heat up the air in the cylinders so that the fuel can combust, and if they are not working properly, it can make starting your car very difficult. Luckily, testing glow plugs is a relatively simple process that you can do at home with a multimeter.

What is a glow plug?

A glow plug is a device used to aid in the starting of diesel engines. When the engine is cold, the glow plug heats the air in the combustion chamber, making it easier for the fuel to ignite. Depending on the type of diesel fuel and other factors the minimum temperature at which diesel fuel will ignite is 52-82 degrees celsius.

How to test glow plug with a multimeter

First, test the multimeter on itself to get the resistance in the cables. This is important off you want to get an accurate measurement. Naturally most cables the resistance will be around 0.02. This should be deducted from the final amount to get an accurate measurement. Then here are the steps below for measuring the glow plug:

1. Disconnect the negative terminal of your battery to prevent any electrical shorts.

2. Locate the glow plugs on your engine. On most cars, they will be located near the cylinders.

3. Using your multimeter, set it to the ohmmeter setting and touch one lead to the tip of the plug and the other to the side of the plug.

4. If the reading is between 0.5and 2 ohms, then the glow plug is working properly. Remember to deduct the resistance in the wires. If it is outside of this range, then the plug may need to be replaced.

5. Repeat this process for each of the glow plugs on your engine.

How to test if a glow plug is working?

Once you have determined that the resistance of the glow plug is within the normal range, you can test to see if the glow plug is actually working. To do this, you will need a 12-volt power source such as a car battery, and the glow plug needs to be out of the car.

Attach one end of a jumper cable to the positive terminal of the battery and touch the other end to the tip of the glow plug. If the plug is working, you should see a small spark or glow. If there is no spark or glow, then the plug may need to be replaced.

It is important to note that some glow plugs are designed to only work when the engine is cold. So, if your engine is warmed up, the plugs may not show any sign of life even if they are working properly.

(Note some manufacturers don’t recommend connecting the battery straight to the glow plug as it may be to much power and cause damage to the glow plug. If you’re going to do this check with your manufacturer.)

How to tell if your glow plug is failing?

There are a few signs that can indicate that your glow plug may be failing:

-Your car is having trouble starting in cold weather

  • There is smoke coming out of the exhaust
  • The engine is taking longer than usual to warm up
  • You see smoke coming from the engine bay
  • The check engine light is on

If you notice any of these symptoms, it’s a good idea to test your glow plugs to see if they need to be replaced.

What is a glow plug tester? and how does it work?

A glow plug tester is a tool that helps you test the health of your glow plugs. It works by sending an electrical current through the plug to see if it lights up. If the light does not come on, then the plug is likely failing and will need to be replaced.

How to use a glow plug tester?

Using a glow plug tester is relatively simple:

1. Connect the positive lead of the tester to the positive terminal of the battery.

2. Touch the negative lead of the tester to the side of the glow plug.

3. If the light on the tester comes on, then the glow plug is working properly. If not, then it will need to be replaced.

How to test the power supply to the glow plug?

In order to test the power supply to the glow plug, you will need a 12-volt power source such as a car battery, and the glow plug needs to be out of the car.

Attach one end of a jumper cable to the positive terminal of the battery and touch the other end to the side of the glow plug. If there is no spark or glow, then the power supply may be interrupted somewhere between the battery and the glow plug.

You can use a multimeter to test for continuity between the positive terminal of the battery and the side of the glow plug. If there is no continuity, then there is an interruption in the power supply and you will need to find and fix it before replacing the glow plugs.

Conclusion

Testing your glow plugs is a relatively simple process that can be done with a multimeter or a glow plug tester. If you notice any of the signs that your glow plugs may be failing, it’s a good idea to test them and see if they need to be replaced. By doing this, you can avoid potential engine damage and keep your car running smoothly in cold weather. If you have any questions about glow plugs or how to use multimeters send us a message.

Toby Ashby

I am an automotive specialist with over 20 years of experience in and around electronics