Common Speed Sensor Problems: Symptoms, Causes, and How to Fix It!

Speed sensor problems can occur over time like any other car components. It can wear down due to normal use but it can also fail because of some wiring issues. If what your vehicle has is a magnetic sensor, it can become faulty from iron sticking to the tip of the sensor. Common symptoms of speed sensor problems include illuminating check engine light, shifting issues, erratic speedometer readings, no cruise control, or the transmission torque converter unable to apply the clutch.

Speed Sensor Problems: What is a speed sensor and how does it work?

To better understand why speed sensor problems occur, we must first understand what a speed sensor is and how it works. The speed sensor is a device that measures the speed of the vehicle at a given time or direction. The gathered data or information will then be sent to the car’s computer. 

The engine control unit uses the data received and calculates it to adjust or regulate other parts that help make the vehicle move like the ignition timing, injection time, the air to fuel ratio in the combustion chamber, and the transmission shift points. It also computes the exact time the automatic transmission has to change gear.  

There are instances where a wheel of the vehicle rotates faster than the other. It is the speed sensor that can alert the engine about it. Issues such as this will alert the ABS or anti-lock braking system to make some adjustments in other related car systems like the brakes, transmission, and drive axles. 

The transmission speed sensor or the vehicle speed sensor is also vital for the accurate operation of your speedometer. You get the correct number thanks to this device. The said sensor is usually found in the gearbox on the output shaft or in the car’s crankshaft. 

There should always be two sensors in the vehicle so the computer can make a comparison of the signals. These two speed sensors work together to provide the accurate transmission data to the car’s computer. The first sensor is called the input shaft speed sensor which is used to monitor the transmission’s input shaft speed while the other sensor is called the output shaft speed sensor. If one of these sensors happens to fall out of alignment or encounters electrical problems, it can affect the entire transmission’s operation. 

Speed Sensor Problems: What happens when a speed sensor goes bad?

Most vehicles today rely on speed sensors to control or manage the engine system. If a speed sensor goes bad, it can send out inaccurate data to the car’s computer that can lead to a number of issues. A faulty speed sensor can trigger many speed sensor problems that can cause these following symptomes:

• Shifting issues.

A faulty speed sensor won’t be able to provide accurate speed signals. When this happens, the car’s computer won’t be able to control the gear shifting within the transmission. This can result in the transmission to shift faster and roughly than usual. Speed sensor problems can also affect the shift timing that extends the transmission shift intervals. 

The hydraulically controlled automatic transmission is built and designed to shift smoothly and when it shifts hard, it may cause problems to its internal components that include the hydraulic lines, valve bodies, and even the mechanical gears. To prevent these problems from happening, you need to contact a mechanic immediately and have your unit checked the moment you notice rough shifting in your transmission. 

• Speedometer is malfunctioning.

There are a lot of vehicles that use vehicle speed sensors as the main input for speedometer operation. When this speed sensor fails, it could result in the speedometer making an erratic reading or at times, no reading at all. Although you can still continue to drive your vehicle without a working speedometer, not knowing how fast you are going will make it difficult and unsafe to drive. It might cause you to have problems with the authorities especially if there are certain speed limits implemented in your area. It can also cause accidents and other problems. 

If you notice that your speedometer suddenly stops functioning, it is an indication that you have a faulty speed sensor. The speed sensor can no longer display the travel speed of your vehicle. It is best that you have it repaired immediately. 

• Illuminating check engine light.

The engine control unit will set off the check engine light and a diagnostic trouble code if the signals from the speed sensors are lost. A check engine light can also be set off if the car’s computer has detected that your tailpipe emission is increasing and is more than the environmental contaminants’ acceptable limits. To know what triggered the check engine light to illuminate, you can connect your vehicle to an OBD-II scan tool. After the speed sensor problems have been determined and fixed, the mechanic will then reset the trouble codes.

• Issues with the cruise control. 

The speed sensors also play a role in monitoring the cruise control since the sensors monitor the input and output shaft speed. Faulty speed sensors that fail to provide accurate data to the car’s computer that can cause it to send an error code to the engine unit control unit or ECU. This can trigger the ECU to shut down the cruise control, rendering it inactive as a precautionary measure. 

This happens since the system will need the speed sensor’s data to keep your car running at constant speed. So if the speed sensor fails to send the signal to the car’s computer, the cruise control will be automatically disabled.  

The moment you notice that you have issues with your vehicle’s cruise control such as not engaging when you press the button, have it checked and inspected by a mechanic to determine whether a faulty speed sensor is the one that caused it. 

• Transmission torque converter is unable to apply the clutch.

One of the common speed sensor problems is the transmission torque converter not being able to apply the clutch and set up a mechanical link between the transmission and the engine. This can happen when the vehicle speed sensor doesn't give accurate information to the car’s computer since the torque converter is activated at a preprogrammed speed. This specific issue can also cause other problems like increased fuel consumption, slipping, and transmission overheating. 

Speed Sensor Problems: What causes speed sensor failure?

Speed sensor problems can set off a lot of issues in your vehicle. You may now be able to notice the signs or symptoms of speed sensor problems, but what causes the speed sensors to fail? Here are some of the reasons why a speed sensor fails.

• Internal electrical fault.

Over time, the speed sensors can get internal damages. This could result in having an abnormal output signal or having no signal at all. 

• Normal wear and tear.

The sensor itself can become damaged or cracked. Its plastic part can also become brittle after being exposed to the elements. The speed sensor’s magnetic part can eventually become worn or damaged.  

• Poor car care and maintenance.

Experts always say that proper car care and maintenance can extend the lifespan of the vehicle as well as its components. Following the recommended maintenance schedule can also help prolong the speed sensor’s life. Failing to do so can increase the risk of speed sensor failure causing your vehicle to experience speed sensor problems. The sensors will not be able to give accurate readings if its parts become covered in gunk, dirt, and other fluid contaminants. 

• Broken wirings and loose connections.

Disconnection of the sensor to the engine control unit can cause problems too. Make sure that you check the connections for loose or broken ones. Check also for corrosions and build ups. 

Speed Sensor Problems: How can you tell if a speed sensor is bad?

If you think that your car is experiencing some speed sensor problems and you want to make sure that it is indeed caused by a faulty speed sensor, you can test using a multimeter. You just need to follow these simple steps. 

• Park your vehicle on a level surface so you can easily access the sensor. Turn the vehicle off and any lights or anything that might draw power from the battery. To make sure that the vehicle is completely turned off, remove the key from the ignition.

• Open your vehicle’s hood and find the speed sensor located near the vehicle’s transmission. You can find the transmission by looking for its dipstick and following it. You should find a small metal sensor connected by two wires, white and black, to the transmission which is held in place by metal bracket. Vehicle speed sensor locations can vary from car to car but it can be usually found on or next to the transmission. If you can’t seem to find it, check your owner’s manual to find its exact location.
• The two wires, black and white, are connected to the speed sensor. One is to ground the sensor while the other one is used to send data or signals to the car’s computer. You need to unplug the wires from the sensor so you can remove it. You can use a small pair of pliers to remove the wires if you can’t grip it with your fingers. 
• A sliding tab or a button can be found on the top or side of the speed sensor. Press the pull tab or button and pull the sensor gently to remove it from its housing.  You might need to wiggle it or slide it out from its base but do not force the sensor since you could damage it. 
• Check if the speed sensor has screws that you need to unscrew to remove it. Unscrew the bolt and the bracket so you can remove the speed sensor. Keep the screws or bolts and make sure that you don’t lose it. 
• Get your multimeter, plug the black lead to the black terminal, and insert the red lead to the red terminal with the letter “V” on it. Gently push the leads into the slots until they “click” into place. You also need to set your multimeter to AC or alternating current by turning its dial.     
• The speed sensor has a slot where it plugs into the vehicle. You need to find a plug that fits into the sensor. You can purchase this wire from an auto supply shop. It has a black ground wire and a white signal output wire.You need to plug these wires securely into the speed sensor.
• Get the black lead wire and fasten it to the exposed wire at the end of the black wire which is plugged into the sensor. Connect the red lead wire to the exposed end of the white wire which is also plugged into the sensor. 
• Since you will be testing a speed sensor, you need to simulate the movement to test it properly. You need to find a drill bit that can fit into the sensor securely to rotate the gear inside it. Put the drill bits into the sensor’s gear slot until you find the one that fits perfectly into the slot. 
• Connect the bit to the power drill and tug it gently to ensure that it won’t fall. Spin the sensor gears using the drill. Allow it to spin at full speed so you will get an accurate reading. You can start slowly, increasing the speed at a consistent pace. 
• While the sensor spins, read the multimeter and check if the number increases with speed. The sensor is faulty when the voltage does not increase with speed or if it doesn’t show any voltage at all.  You will need to replace your sensor to fix the speed sensor problems. 
• Reinstall the speed sensor into your vehicle. If it needs replacement, make sure that you replace it with the same make and model to ensure that it will fit. 

Although you can tell that your speed sensor is bad when you experience the common speed sensor problems or symptoms, having it checked by a mechanic to get a proper diagnosis is still recommended. However, if you want to save money from repairs, you can test it yourself and replace the sensor yourself when needed. You just need to use the right tools and get the right speed sensor replacement.