How to test a tachometer with a multimeter

Having a faulty tachometer in your car can be very dangerous. You could end up without your driver’s license and not be able to go to work if you have no other means of going than by your car. You could also drive at speeds that are not adjusted to current road conditions and end up on the side of the road when it rains because you thought that you are going slower than you actually are.

Car mechanics can prevent all of these things by checking your vehicle regulary, but if you want to save a few dollars, you can do something too.

Steps to test a tachometer with a multimeter

Fluke 116 HVAC MultimeterHere’s how: You will need a multimeter and a couple of screwdrivers. I recommend that you buy a quality tach probe for the multimeter since probes that are shipped with multimeters are usually of not so good quality. It is also imperative that you calibrate your multimeter before you begin with the testing.

Unlike other techniques for testing a tachometer with the multimeter (Check multimeter in Amazon which we using in this test), this one won’t require you to open up the tachometer nor will it require you to open up your dashboard.

Here’s the deal: You need to open the hood of the car and locate the ground wire. Ground wire is usually visible on a thin part that leads from one side of the car to another, located between the engine and the body of the car.

Locate the wire box: Once you have located the ground wire, it will lead you to the breaker box. When you have located the box, locate the wire that leads to the tachometer. There is no instructions on how to locate the wire that leads to the tachometer because it differs from one manufacturer to another. The only possible thing that you can do to locate it, unless you are a mechanic, is to try each wire with the multimeter to see if that is the one.

If you are the car mechanic, if your experience is not helpful, you should look up google and see if you can find plans for the car, but that’s probably a long-shot.

Test the tachometer: 

car tachometer

  • Take your multimeter and insert the tachometer probe in the multimeter.
  • Set the multimeter to AC current and touch the tachometer wire that leads to the breaker box with the engine on.
  • Have one of your friends sit in a car and tell you when the tachometer dial reaches certain points that are important for your calibration process.
  • At the same time, the multimeter will display accurate results. You can then compare the two results to see if the tachometer is precise and if it isn’t, it’s best that you go to the mechanic and replace it ASAP.

Tips

I recommend that you wear gloves while doing this because of a small possibility of electrical shock.

Make sure that you explain to your friend that he should tell you the values that are displayed at the tachometer as soon as possible in order to get accurate results.

If you feel overwhelmed by the number of objects that are under the hood, that’s OK. In that case it’s probably best to let the mechanic do the job for you.

Sometimes the cause of a faulty tachometer can be in the pure fact that your car is low on gas. I won’t go in the details of it because it’s complicated, but make sure that you have a full tank of gas before doing this. This happens very rarely.


I hope that this guide has helped you to determine the accuracy of your tachometer and maybe even helped you to save a couple of dollars at the mechanics, since you already know what is wrong with your car.

If you have discovered that your tachometer is indeed faulty, all that is left to do is that the mechanic replaces the tachometer and you are good to go!

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