5 Common Failing Speed Sensor Symptoms

Naomi O'Colman

Common Failing Speed Sensor Symptoms

Common Failing Speed Sensor Symptoms

Speed sensor or vehicle speed sensor (VSS) is an intricate system. There will be times it malfunctions. Do you know the failing speed sensor symptoms yet? Knowing these signs will help us take action on time.

Basics Understanding of VSS

Transmission speed sensors measure the rotational speed of transmission. It is a system that measures the speed at which the engine is running. This sensor is calibrated to measure the rotational speed of a drive shaft at various speeds. The transmission speed sensor reads this information and sends it to the vehicle’s Electronic Control Unit (ECU).

In simpler terms, this system allows us to calculate the vehicle’s speed from its engine RPM which in turn calculates how fast we want our car or truck to be going at any given moment.

Input shaft speed and output shaft speed are precisely detected by these sensors. This is done by the use of electronic pulses. The pulse sends information to the vehicle’s ECU in order to control the engine speed and in turn, control the car or truck’s speed.

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The VSS system is used for controlling engine speed when the vehicle’s brakes are applied. This way, power can still be transmitted to the wheels while applying brakes.

When the whole system doesn’t cooperate with each other, the following symptoms might occur.

5 Common Failing Speed Sensor Symptoms

#1 Check Light Engine Turning On

The first sign is to detect if the service engine light becomes illuminated due to faulty VSS. This happens because the vehicle’s ECU does not receive the speed information from the sensor.
Remember that Check Light Engine On can be caused by many factors as well. So, have a mechanic check your car. If the problem is due to failing VSS, it will need to be replaced.

#2 Malfunction of Speedometer

The most common sign is that the speedometer becomes erratic or inaccurate especially around 50mph and around 70mph. This is also caused by the malfunctioning of the VSS. Because it is the system that sends the signals to control engine RPM, it creates bad readings on your vehicle’s speedometer.

Because of the malfunctioning of this system, a car will not be able to display accurate speed. This is an indicator that VSS must be replaced.

#3 Sign of Engine Stall

This does not only happen when the engine gets slower but also during acceleration.
For this, check if your vehicle exhibits a stumble or lurch while accelerating or decelerating the faster it goes the faster it will stumble and lurch. Then, check if your vehicle uses gas gradually becomes less and less every time you accelerate.
If these symptoms occur, you should check if your VSS has already been replaced. If not, get it replaced right away.

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#4 Engine Shudder

It has been said that if your vehicle engine shudders, it could be caused by a bad speed sensor. As we know, the speedometer is electronically connected to the VSS so an erratic reading will cause erratic speeds and this will cause the engine to shudder.

#5 Cruise Control Stop Working

If the cruise control stops functioning, then you know that it can be a sign of a bad speed sensor. You will then need to check the way it works. When the sensors send error codes to the ECU, it will inactivate the cruise control for safety.


It is important to know these common failing speed sensor symptoms. Our goal would be to replace the broken part without delay. Don’t let your vehicle experience slipping or shudders, check if any of the symptoms are caused by VSS problems.
If you think you have encountered this problem before, bring your car to a mechanic to check it out.