How to test your glow plugs?

The operation of glow plugs

The purpose of glow plugs is to help you start your diesel vehicle faster. However, if you find it difficult to start the engine of your car, it may be because of faulty glow plugs. To check the condition of your candles, here's  how to test a glow plug . 

You can also apply the following method before going to the garage.

Test the glow plugs with a multi-meter

As a first step, know that you can test your glow plugs yourself without the help of a specialist. To do this, you will simply need to bring a digital multi-meter.

Calculate the resistance of your multi-meter

Once you have your multi-meter, first place the slider on the ohm scale. That is to say the part materialized by the sign Omega (Ω). Then, measure the resistance of your multi-meter to know the value to subtract when you have made the necessary measurements on the glow plugs of your car. To do this, all you need to do is touch the metal tips of the two cords (red and black) together and then read the value on the meter's display.

Test the battery

Then test the battery voltage of your car to see if the problem is not there. Indeed, it is the battery that will power your glow plugs. Thus, they may not work if your battery is faulty. All you need to do is set your multi-meter on the DC scale (DC sign). Then touch the corresponding terminals of your battery with the cords of the multi-meter (black cord on the negative terminal and red cord on the positive terminal). You must obtain a value between 12.5 and 13 volts. If this is not the case, the problem certainly comes from the battery.

Connect the multi-meter to the candles

If you get these values, you can continue and put your multi-meter back on the ohm scale. Then take the technical manual of your car to locate the locations of the candles. Once spotted, remove the caps that protect the candles. It will then touch a mass with the metal end of the black cord. To do this, you can also locate the location of one of the two masses on your manufacturer's manual. Then touch the glow plug with the tip of the red cord and without taking off your second cord from the ground. Finally, you just have to read the value on the multi-meter. If the latter is between 0.6 and 2 ohms, it is that everything is fine. However, if you see lower or higher values, you must change your candles! Do not forget to subtract from the result obtained, the resistance value of your multi-meter calculated at the beginning.

If there is really nothing to do and your candles work but not your engine, the ultimate recourse is of course to go to a mechanic who will be able to help you.