What Are The Symptoms Of A Bad Speed Sensor?

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When something goes wrong in a car, you are bound to notice different signs. Now, this leads to the question, “what are the symptoms of a bad speed sensor?”

Maybe your car is currently not functioning as it used to, and as part of troubleshooting the problem, you wish to know if the wheel speed sensor is the culprit?

There are many signs that indicate your vehicle’s speed sensor(s) is faulty or already damaged. We have mentioned some of these signs – the commonest ones – in this article.

Also, this article tries to explain the functions of speed sensors and what they could cause if they go bad.

What Are The Symptoms Of A Bad Speed Sensor?

The basic, and arguably the only function of speed sensors is to read your vehicle’s wheels’ speed and rotational movement and sends the information as “signals” to the ABS.

These signals are processed by the ABS and utilized to modify your car’s engine performance.

Hence, when one or all of your vehicle speed sensors goes bad, you will notice a significant drop in your engine’s performance, and there are other issues you are likely to experience too.

Below are the signs/symptoms of a bad speed sensor.

Symptoms Of A Bad Speed Sensor

Symptoms Of A Bad Speed Sensor

1. Wrong Speedometer Reading

Since it is the speed sensor that sends information about the speed of your car wheels, when it is bad, apparently, it’d send wrong information, which can result in erratic speedometer reading.

When your speedometer isn’t giving you an accurate reading, it would negatively affect how you drive.

2. Driver Assistance Features/Techs Would Stop Working

The moment your vehicle’s speed sensor is faulty, one of the systems that is affected immediately is the driver assistance systems.

Features such as cruise control would not engage anymore. If there are other driver assistance features available on your car, they’d stop working too.

3. Transmission Issues

Faulty speed sensors can directly affect your car’s transmission, especially if your car runs with an auto transmission.

You will notice that your car doesn’t accelerate as before, as well as experience delayed shifts, hard shifts, and all that.

These issues occur because the speed information relayed by speed sensors is utilized by The transmission Control Module (TCM) to determine shift timing.

Hence, when wrong or no information is passed, your auto transmission engine would react according to the signal it got, and the result would be delayed shifts, hard shifts, or other possible issues.

4. Check Engine Light Would Appear

The check engine icon doesn’t get illuminated unless your vehicle’s computerized systems have detected an issue with your engine.

While there are so many reasons that could cause the check engine light to appear, a bad speed sensor can also cause that to happen.

To know the exact reason why the check engine icon got illuminated on your dashboard, use an OBDII scanner and troubleshoot.

5. Hard Braking

Another common symptom of a faulty or bad speed sensor is difficulties in applying the brakes.

When your brake petals seem very hard to match down, it could be that your speed sensors are bad and need replacement.

What More?

These symptoms do not only apply to bad speed sensors – but they are also symptoms of other possible faulty components of your car.

Hence, the best way to be sure that your speed sensors are actually bad is to troubleshoot.

Vehicle Speed Sensor Troubleshooting

There are a couple of ways to troubleshoot speed sensors; you can use an OBD II scanner, voltmeter, or even run the test manually as shown on the video above.

However, the best-recommended method is using an OBD II scanner – this way, you will get more accurate results.

Here’s how to test vehicle speed sensors manually:

  • Turn off the vehicle completely, ensure that you are parked at a safe corner.
  • Locate where your vehicle’s speed sensors are installed (the location of speed sensors differs from car to car – consult your car manual to know where they are installed on your vehicle).
  • Disconnect the wiring harness connector from the VSS
  • Pull the sensor from its housing. Again, different sensors are protected differently – don’t try to pull out the sensor forcefully, do it gently and check for screws  – some sensors are guided with screws.
  • Connect the speed sensor to a multimeter and set the meter to AC
  • Now, find a drill bit that fits into the VSS
  • Connect the bit to a power drill
  • Engage the drill and check the readings that appear on the multimeter.
  • If the voltage doesn’t increase, the sensor is faulty or dead, but if the voltage increase with speed, the sensor is good.


Hopefully, this article answers the question, “what are the symptoms of a bad speed sensor?”

If you find the troubleshooting process to be challenging or too technical, endeavor to have a mechanic do that for you. Also, we’d advise that you try to fix any issue with your car as fast as you could.

Why? it is best to act proactively so that the little fault does not escalate and turn into a costlier repair.

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