How to Check a Tachometer

Co-authored by Audra Fordin

Last Updated: December 23, 2022 References

If something seems off with the gauges on your car, motorcycle, or boat, checking the tachometer, which measures the engine's revolutions per minute, is a great first step. This wikiHow article will walk you through reading and testing your tachometer to help determine your vehicle's issue.

Method 1

Method 1 of 5:

How do you read a tachometer?

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Note which number the needle on the gauge points to. An analog tachometer looks like a semicircle with the numbers 1-8 on it. Simply multiply by 1,000 to get the actual number of RPM. For example, if the needle points at 2, that is 2,000 RPM. As the engine revs, the needle moves between the numbers.^{[1]
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- A digital tachometer is more precise and shows the engine speed in actual numbers rather than looking at the needle. It looks like a digital clock. You might see a number like 2,000 or 2,147 on the display.

Method 2

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How do I know if my tachometer is bad?

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Check to see if the tachometer moves before looking for other problems. One obvious issue is if your tachometer is stuck on zero or any other number. If it doesn’t give any other rating even when your engine is running, it’s not working.^{[2]
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Monitor whether the needle seems to be moving erratically. If you’re moving at a steady speed, the needle shouldn’t be jumping around (or the digital display shouldn’t be changing rapidly). If it is, it’s a sign the tachometer is bad.^{[3]
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Notice if the RPMs seem to be consistently off when you are driving. For example, if you are moving at a fast speed in your boat, but the tachometer is showing a 1, it’s probably not working.^{[4]
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- A low number like a 1 or 1.3 on an analog or digital display can indicate a problem with the tachometer.

Method 3

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What makes a tachometer stop working?

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Most tachometers stop working simply because of age. Sometimes newer models will stop working properly if there is a problem with the LED display (if they have one).^{[5]
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Research source} If you suspect you have a problem with your tachometer, start by checking your owner’s manual. It can help you troubleshoot the problem if your display isn’t working or if your readings seem off.
- The manual will probably tell you to start by checking the fuse for the tachometer. If it’s blown, that’s likely what’s wrong with the tachometer. If you feel comfortable doing so, you can change the fuse yourself. Pick up a new one at an auto parts store or order one online.
- If you are handy, you can use the manual to find the tachometer and check it out for yourself. Take a look at the wires on it. If they look frayed, damaged, melted, or burnt, the tachometer probably needs to be rewired.
- Call a mechanic if you need a new tachometer or wires. It’s always best to get an expert’s help. If you have some experience with automotive, you can try replacing the wires yourself first. Check an auto parts store to get the parts you need.

Method 4

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How do you test to confirm a good signal?

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Use a handheld tachometer to test your engine’s tachometer. You can purchase one of these at an automotive or boat parts store, or find one online.^{[6]
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- Follow the directions in the manual for the handheld tachometer to it attach to your engine. Turn on your motor and rev your engine so that it reads 1,000 RPM on the handheld device.
- If your engine tachometer is within 10% of the same reading as the handheld device, your tachometer works fine. If it’s outside of that range, you need to call a mechanic or try to troubleshoot the problem yourself.
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Test the tachometer using a multimeter. Make sure you have a basic multimeter (available online and at auto parts stores) and your car/boat manual available. Use the manual to help you find the wire that connects the engine to the tachometer.^{[7]
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- Locate the tachometer probe (again, consult your manual) and insert it into the multimeter. Rev your engine. If the tachometer reading and the multimeter reading match (or are within 10% of one another), it's working properly.^{[8]
  X
  Expert Source
  
  Audra Fordin
  Certified Automotive Technician
  Expert Interview. 13 January 2022.} If not, it's time to troubleshoot.
- If you have absolutely no idea what you're doing, call a friend for help or contact a mechanic. It's okay to not know!
- It's also possible that the tachometer isn't the problem. If it tests okay, let the mechanic know you've already checked out that possibility. Describe the problem to them so that they can check your car or boat for other issues.

Method 5

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What is a normal tachometer reading?

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A good tachometer reading is one that is steady and doesn’t fluctuate too quickly. When your engine is idling, your RPM should be between 1,000 and 1,500. When you accelerate, the needle will go up. But as you reach a cruising speed, the RPM should become steady and your tachometer should settle in between 1,500 and 2,000.^{[9]
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- Don’t worry if the needle or digital reading goes up dramatically if you speed up quickly. It will adjust as your speed adjusts.
- Most tachometers show a “red zone” that indicates you’ve revved your engine too much. This typically happens when your RPM is 7,000-8,000. If you hit that area of the gauge, slow down.