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4 Common Bad Speed Sensor Symptoms


It is the job of your car’s engine management computer to monitor vehicle speed.

It needs to know how fast the car is moving to make decisions regarding transmission shift and cooling fan operation, among other things. This critical data is usually provided by the vehicle speed sensor (VSS), which is located on the transmission of some vehicles or behind the instrument cluster of others.

So, if this device were to malfunction, you will experience a raft of problems. You can identify these problems by looking out for bad speed sensor symptoms, such as erratic shifting.

Keep on reading to know what symptoms to look out for!

What Is a Vehicle Speed Sensor?


vehicle speed sensor




This is a detection device used to monitor the speed of whatever shaft is driving your wheels.

The vehicle speed sensor is sometimes found in the instrument cluster, but most manufacturers mount it on the transfer case or transmission. In some cars, the transmission speed sensor is used instead of the vehicle speed sensor.

The speed readings from the vehicle or transmission speed sensor are conveyed to the engine computer. Data from the sensor is used to manage shifting points, control your speedometer, and fine-tune the fuel mixture. It is also used with advanced engine functions, such as cylinder deactivation. 

When it is time to replace a bad speed sensor, gaining access to it could be harder than you had imagined. Some vehicle speed sensors are easy to get to once you get under your car. But others may require you to uninstall other components.

This is especially true for front-wheel-drive cars because the VSS might be mounted on top of the transmission. Some speed sensors come equipped with gear on one end. So, you have to be careful when installing such a VSS.

Bad Speed Sensor Symptoms

You can tell if your VSS is faulty if you observe any of the following bad speed sensor symptoms:

Speedometer Malfunction

The speedometer reflects the speed of your vehicle. It is normally combined with the odometer, a device that records mileage or the distance the vehicle has covered so far.

speedometer with check engine light



If the speed sensor is bad, it will be unable to tell the speedometer and odometer how fast the car is moving and how far it has gone. The needle of the speedometer will bounce up and down. Erratic speedometer readings will negatively affect how you drive your vehicle.

However, you should note that there are other causes of a faulty speedometer, including poor connection, faulty computer, broken gear, and bad wires.

Improper Shifting

When you’re having problems changing gears, you probably have a bad speed sensor. 

Your car’s speed sensor conveys signals to the engine control module. The computer of your vehicle uses the signals from the speed sensor to determine when the transmission has to shift gear. A bad speed sensor, therefore, can lead to erratic shifting, which causes the transmission to shake, jerk, or shift hard during a shift change.

automatic transmission shift control



You could experience delays in shifting. This usually happens between shifting gears or when going into gear and the engine could rev really high before shifting. The transmission may also not achieve the desired gear or may not go to overdrive.

Cruise Control Stop Working

Cruise control is an advanced system that holds your vehicle at a specific speed. This unique driving feature is usually used on faster roads or highways to take some pressure off the driver.

cruise control push button switch and dashboard image



When you press the button to activate cruise control, signals from the driveshaft, speed sensor, speedometer cables, and electronically produced engine pulses are used to understand the speed of your vehicle. So, without signals from the speed sensor and speedometer cables, the cruise control could simply stop working.

Check Engine Light

When you have a bad speed sensor, the check engine light will display on the dashboard. A scan tool will show several codes, including P0503, P0502, P0501, and P0500 among others.

can obd tool testing for vehicle speed sensor



The P0500 diagnostic code indicates a malfunctioning vehicle speed sensor. You can drive for short distances with a malfunctioning speed sensor, but a replacement is necessary. The P0501 code specifies that you’ve got an erratic voltage output or the vehicle speed sensor is out of range. 

How to Diagnose a Bad Speed Sensor

The most common place you will find a vehicle speed sensor is in the transmission system. So, you need access to your vehicle’s transmission. You can do this by lifting your vehicle.

Then look for the wiring in the transmission, one of the cables will lead you to the position of the speed sensor. Undo the bolt holding the sensor in place and also detach the connector harness. Test the electrical contacts in the connector harness to see if there is any power.

The first thing you have to do is turn on your ignition key. Use a digital multimeter equipped with alligator clips to test if there is any power in the harness. The black lead is the ground and the red lead goes to the connector harness.

Set the multimeter to DC voltage and take the reading. Any reading on the multimeter indicates there is power in the harness and your speed sensor is bad. So, the most ideal thing to do is replace the bad speed sensor with a new one.

Check your owner’s manual for the correct part. Most auto part stores will use your vehicle’s make and model to get you the correct part.

Related: Find out the problems if your vehicle smells like vinegar

FAQs

What is the difference between transmission and vehicle speed sensors?

A vehicle speed sensor is used when talking about cars in general. A transmission speed sensor, on the other hand, is used when dealing with vehicles with automatic transmission. Both sensors monitor the speed of the vehicle at different shift points and report the information to either the engine control module or the transmission control module.

What sensor type is a vehicle speed sensor?

A vehicle speed sensor is considered an output speed sensor. Its main job is to tell the control unit of your car how fast the car is moving. The speed information is then displayed on the speedometer. A vehicle speed sensor can either be optical or inductive. The most common design is inductive.

What is the replacement cost of a vehicle speed sensor?

The cost of replacing a bad speed sensor may range from approximately $250 to $300. Labor costs, on the other hand, may range from about $150 to $200. A do-it-yourself replacement could be a cheaper option. 

Is it safe to drive with a bad vehicle speed sensor?

You may be able to drive with a P0500 code for a short distance before getting a VSS replacement. But it isn’t recommended because the problems could multiply and lead to several issues, including difficulty in changing gears and incorrect speedometer readings.

Conclusion

Your vehicle speed sensor is a very important device in your car, which plays a vital role in maintaining optimum performance and fuel economy. If it goes bad, you should expect some problems like incorrect speedometer readings, erratic shifting, and check engine light. All these symptoms are easy to note if you can identify them. We hope this information has equipped you with the necessary tips you need in case you experience a bad speed sensor.



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