How to Quick Test a Spark Plug for Vehicle

When any of small equipment fails, one of the first things we check is the spark plug. This article will show you guide on how to quick test a spark plug by multimeter.


A spark plug always has a number on it. This bad one is RC12 YC at the bottom.


The one we are going to using for replacement shows a different number here BK R5E.


But on the packaging it shows the RC12YC which matches the original number.


If you have a spark plug that has an “R” ,that means there is a resistor inside the spark plug. Resistors are made to keep it from interfering with things such as a car radio or a camera. So a lot of times they’re not found in spark plugs that are used on lawn equipment.



To test for ohms you need to change your multimeter to the ohms setting.

On ours it’s indicated by the letters O H M, on some multimeters it’s indicated by the horseshoe symbol upside down horseshoe or Omega if you’re familiar with the Greek alphabet. We like the 20K setting, anything between 10 and 20k is fine. If you don’t have 202K you can always go up higher.


Touch one of the leads to this end of the spark plug and remember there’s a metal piece that goes all the way through the center of the spark plug and there is a resistor inside the metal piece .


the other end of the spark plug has little tip on where is we want to touch our other lead.


Touch leads together to start


It shows zeros that means multimeter is functioning properly.

Test the new spark plug


It shows 6.00. all reading of ohms are actually in thousands. So when we say 6 ohms, we’re referring to 6 thousand ohms. Anything between 5 and 15 ohms is pretty normal for a spark plug made for a small engine.

Test the bad spark plug.


We get no readings. That means something inside is broken. It could be the resistors gone bad or that there’s a crack in the metal piece or a crack in the insulation.

One thing you need to be careful for is if you have a dirty old spark plug it could have some carbon buildup, so you need to take a wire brush and clean tip of the spark plug or you can also spray some brake cleaner on it to get it nice and clean.

If you hire someone to replace it, it will cost a lot and so not profitable. Because is so easy to do it, so i share this guide on how to replace spark plug correctly by yourself.

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