Like other vehicle sensors, transmission speed sensors can be delicate and impacted by heat, dust, and fluid contaminants. However, a bad transmission speed sensor can impact the gear shift, torque converter function, and even the vehicle’s cruise control function.
Key Takeaways
The following are the key takeaways from this article:
- The transmission speed sensor collects information about the car’s speed and sends it to the ECU for the desired function.
- It is located on the outer shaft. However, its position can change depending on the vehicle’s model, make, and variant.
- The common causes of bad transmission speed sensors include wear and tear, loose connections, internal electric faults, and improper maintenance routine.
- The common symptoms of a bad transmission speed sensor include disengaging cruise control, erratic torque converter, malfunctioning speedometer, erratic gears, and stuck gears.
- The common solutions for transmission speed sensors include cleaning the sensors, replacing the faulty sensors, and resetting the DTC.
- The cost to replace a faulty sensor is around $200-400.
Introduction
Automatic transmission is always dependent upon other sensors that can result in gear shift at the right time.
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One such sensor is the transmission speed sensor. This sensor is located on the outer shaft and is responsible for gear shift at the right time depending upon the car’s speed. This sensor has a magnetic, electric system encapsulated inside a plastic body.
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So, it is an important sensor for sensing speed and sending information to ECU regarding gear shift (1). This article will further analyze the causes of bad transmission speed sensors’ causes, symptoms, and solutions.
Purpose of Transmission Speed Sensor
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As the name indicates, a speed sensor collects information about the car’s speed. The analysis of the movement of the input and output shaft does it. The sensor then compiles information and sends signals to the car’s ECU to take certain steps.
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These steps can send information to the transmission control unit to switch gears. Similarly, the transmission speed sensor will control the speedometer and other components, such as the vehicle’s cruise control (1). It is a simple sensor that sends information about the vehicle’s speed to ECU.
Causes of Bad Transmission Speed Sensors
Following are a few common reasons for bad transmission speed sensors:
Wear and Tear
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Normal wear and tear can be a major reason for the failure of the transmission speed sensor.
Transmission sensors are capsulated in a plastic shield, and the magnetic part of the sensor is located inside. The plastic part can become brittle after exposure to heat and dirt over time. This can impact the sensor’s function to sense speed and send the right information to the car’s ECU (2). Similarly, the magnetic part of the sensor can be damaged, which is responsible for measuring the exact speed information. This damage can aggravate over time, impacting the sensor’s ability to work. Along with wear and tear, dirt can deposit over the transmission speed sensor, hindering its functioning.
Loose Connection
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Another cause of a bad transmission speed sensor can be a loose electrical connection. Sensors send information in the form of voltage to the ECU, which is then detected, and ECU directs the transmission control unit to shift the gears.
However, a bad/loose connection can impact the readings of the speed sensor. Disconnection of the wire with the ECU can also be problematic. Similarly, corrosion can build up over time on the wire connections, impacting the sensor’s functioning (1). The wires can also melt due to overheating. So, check for every possible connection error impacting the sensor’s ability to transmit the signals.
Internal Electric Fault
Sensors have several small electrical components inside. Damage to a small component can impact the sensor’s signals. With internal electric faults, the sensor can send no or wrong signals to the ECU.
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If you observe an erratic gear shift with the sensor and its connections look normal, there is a chance of an internal electric fault within the sensor.
Improper Care/Maintenance of Transmission Components
A service schedule is an important part of car maintenance. The service schedule does replace not only dirty/contaminated fluids of the car but also resolves small problems related to the car’s sensors and other electronics (2). The car manufacturers set service maintenance time according to the life of certain components. Sometimes, service maintenance also includes cleaning sensors and other small electrical components that can send a wrong signal due to dirt, contaminants, and other fluid buildups on them (1).
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Improper care/maintenance of the vehicle can thus impact the lifespan of the speed sensor and other electrical components.
Symptoms of Bad Transmission Speed Sensor
Following are a few common symptoms of a bad transmission speed sensor:
Cruise Control Disengaging
Cruise control is a feature in your vehicle that will auto-accelerate the car and maintain the desired speed. This feature is used for the driver’s convenience and to increase the vehicles’ fuel mileage on long routes. First, however, the sensors must be positioned to engage cruise control.
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The transmission speed sensors record and send information about the speed of the input and output shaft so that the transmission control unit can shift gears accordingly. However, a bad speed sensor will send an error code to ECU, and the cruise control will be disengaged as a safety precaution.
The speed sensor is required to constantly send a signal to the ECU to maintain cruise control. So, if you are observing erratic behavior with the cruise control or it is not engaging by pressing the cruise control button (3). Then it is recommended that the driver take the car to a professional service center to get the speed sensor replaced.
Torque Converter Issues
Torque control acts as a clutch in automatic transmission vehicles. When the speed sensor sends information to ECU, it engages the torque converter as a clutch that shifts the gear (5).
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However, a malfunctioning speed sensor can have an adverse impact on the torque converter and the vehicle’s transmission system. It can cause the transmission system to overheat as the car might get stuck in a single gear.
Similarly, it can increase the vehicle’s fuel consumption, as the gears are not changing according to the load requirements. You can also face transmission slipping due to a malfunctioning speed sensor impacting the torque converter.
Malfunctioning Speedo
Sometimes, your vehicle’s speedometer might also stop working when the transmission speed sensor goes bad. The vehicle’s speedometer uses the same transmission speed sensor to depict information about speed and RPM (3). Speedometers can also show erratic readings that can impact drivers’ decisions. For example, the driver will be unaware of the actual speed and might increase the vehicle’s speed causing accidents. Similarly, the driver can face legal action for crossing the speed barrier in areas with strict speed restrictions. In such cases, the importance of a properly functioning transmission speed sensor increases.
Stuck Gears
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A common symptom of a malfunctioning transmission sensor are the stuck gears. This is because some modern vehicles are installed with a failsafe that prevents the transmission from shifting gears when the ECU detects any electrical error.
This is called limp mode, where the vehicle gets stuck in a particular gear. In this case, it is unsafe to drive the vehicle and can become more frustrating if your car is stuck in neutral/parking gear (4). So, you have to tow the vehicle to the service center if the vehicle enters limping mode due to an erratic transmission speed sensor.
Erratic Gear Shift
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The final symptom of a bad transmission sensor can be erratic gear shifting. The vehicle’s ECU and transmission speed sensor work together to choose the right gear for the vehicle.
This depends upon the vehicle’s speed and RPM load conditions. When the transmission sensor fails, you might experience the engine stalling or revving unexpectedly. Continuously mismatching gears can also impact the vehicle’s driving comfort, as it might become jerky/shaky (3). So, consult your mechanic when the vehicle faces an unstable gear shift situation, as it can adversely impact different transmission/engine components.
The solution to Bad Transmission Speed Sensors
Following are a few solutions to bad transmission speed sensors:
Clean the Transmission Sensor and Test Drive
The transmission speed sensor is mostly located on the rear of the output shaft. Again, you can consult the vehicle’s instruction manual, as its position can vary depending on its make and model (5).
After locating the transmission speed sensor, try cleaning it with a soapy water solution. When the transmission sensor seems clean, try to test drive the vehicle.
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As discussed above, you are all good to go if you face no symptoms of a bad transmission sensor. However, if the symptoms reappear, it is recommended to replace the sensor.
Replace the Faulty Sensor
Another common solution for bad transmission sensors is their replacement. As discussed above, overheating and long-term driving can impact the plastic and magnetic part of the sensor, which can impact its reading.
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So, try replacing the speed sensor and test-drive the vehicle (4). You can also consult the vehicle’s instruction manual to learn about the general sensor lifespan and its maintenance/replacement procedure. The sensor specifications are also provided in the vehicle’s instruction manual. So, you can order a senor online by analyzing its specifications.
Reset the DTC and Test Drive
Sometimes, the transmission sensor might send some wrong information to ECU that might illuminate the check engine/check transmission light (5). In this case, you might not experience any other specific symptoms except for the warning lights on the vehicle’s dashboard.
You can try resetting the DTC using a hand-code reader. However, test-drive the vehicle before reaching any conclusion. The sensor can have problems if the DTC and warning light appears again.
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So, replace it before it causes internal transmission/engine damage.
Conclusion
To conclude, a transmission speed sensor might seem like a small component, but it has an important role in the gear shift. This sensor collects information about the vehicle’s speed, and the ECU directs the transmission control unit to change the gears accordingly. However, dirt/fluid contaminants can stick over the sensor impacting its performance. Similarly, loose wiring and overheating can cause the sensor to send wrong signals to the ECU. In any case, get the sensors replaced or cleaned before it causes irreparable damage to the vehicle’s transmission or other engine components.
FAQs
Disengaging cruise control is only sometimes due to a bad speed sensor. Although, the speed sensor collects important information that helps ECU to engage the cruise control. But certain problems in the ECU, cruise control module, and wiring can also cause the cruise control to disengage. So, look for symptoms that illustrate a bad transmission speed sensor and disengaging cruise control.
Well, there are different signs that the transmission sensor has gone out. But one major sign is the erratic gear shift or the gear shift in one particular position, is the limping mode. When a transmission sensor goes out, the transmission control unit gets the wrong signal from the ECU, and there is an erratic gear shift in your vehicle. You can also experience your car stuck in neutral or 2nd gear, called limping mode. In any such case, you should only drive the vehicle for a short distance before resolving the issue.
Transmission overheating can be due to several reasons, the main reason being less transmission fluid. However, when a sensor goes out, it will cause the gears to stick. When the gears are stuck, it can exert more pressure on the transmission system, which will overheat. Driving long distances with heated transmission can cause damage to the gears that will ultimately require the replacement of the entire transmission system.
