What Happens When A Transmission Speed Sensor Goes Bad? (Answered)

In the detailed mechanics of a vehicle, the transmission speed sensor holds significant importance. This integral component of your vehicle’s transmission system plays a vital role in monitoring and transmitting critical data about the car’s rotational speed to the vehicle’s onboard computer system. Its flawless operation is fundamental to the smooth and efficient running of your vehicle.

However, the question arises – what happens when this essential speed sensor goes bad? The malfunction of a speed sensor can lead to a host of problems, extending from erratic shifting to a decline in engine performance.

In this comprehensive article, we delve deep into the relevance of the transmission speed sensor, the possible symptoms, and the potential aftermath of its failure. Furthermore, we guide you through the processes of diagnosing and replacing a faulty sensor.

Problem Solution
Erratic shifting or difficulty in shifting gears Diagnose the speed sensor using a scan tool and replace if necessary.
Inaccurate or fluctuating speedometer readings Inspect the speed sensor for damage or loose connections. Replace if needed.
Reduced engine performance and power output Replace the faulty speed sensor and ensure proper calibration.
Transmission stalling Check the speed sensor for damage or electrical issues. Replace if required.
Activation of the MIL or check engine light Scan the vehicle’s computer system for trouble codes and diagnose accordingly. Repair as necessary.

Understanding the Transmission Speed Sensor

At its core, the transmission speed sensor is a monitoring device installed in your vehicle. Its primary role involves assessing the rate of rotation of your car’s gears and communicating this critical information to the computer system. Subsequently, this data plays a pivotal role in controlling key functions such as fuel mixture, ignition timing, and the determination of transmission shift points.

Without a well-functioning speed sensor, the performance of a vehicle could be severely impacted. In essence, the sensor serves as the vehicle’s ‘eyes,’ ensuring optimal operation at all times.

How the Speed Sensor Measures Rotational Speed

The speed sensor employs a magnet to process information about the rotational speed of the gears in your vehicle. As the gear teeth pass by the sensor, they induce changes in the magnetic field.

These changes are then converted into electrical signals that represent the speed of the gear. This crucial data is decoded by the car’s computer system, which uses it to make necessary adjustments in various vehicle operations, thereby maintaining optimal performance and efficiency.

For an in-depth understanding of how the speed sensor works, you might find this comprehensive guide here useful.

Transmission Speed Sensor Types and Locations

Owing to the diverse range of vehicle types and models, the type and location of the transmission speed sensor can vary significantly. Despite this variation, most vehicles typically have two types of sensors: the input speed sensor, which monitors the speed of the transmission input shaft, and the output speed sensor, which keeps track of the speed of the output shaft.

These sensors are usually located on the transmission casing and are connected to the vehicle’s computer system through electrical wiring. Their position can vary based on the make and model of the vehicle, but they are typically found near the front or side of the transmission.

Understanding the location of these sensors in your vehicle can significantly simplify the process of diagnosing and resolving potential issues.

What Happens When a Transmission Speed Sensor Goes Bad

Shifting Problems: Erratic Shifting or Difficulty in Shifting Gears

One of the most prominent symptoms of a faulty transmission speed sensor is shifting problems. These issues can manifest as erratic shifting or difficulty in shifting gears. Since the transmission speed sensor helps determine when to shift gears based on the vehicle’s speed, a faulty sensor may send incorrect signals, leading to erratic or harsh gear shifts.

Drivers may experience sudden upshifts or downshifts, and the vehicle may even shift into neutral for no apparent reason. Furthermore, in automatic vehicles, a failing speed sensor might cause the transmission to stay in a single gear, inhibiting normal shifting.

Speedometer Issues: Inaccurate or Fluctuating Speedometer Readings

Another significant symptom of a bad transmission speed sensor is issues with the speedometer. If your speedometer is acting erratically, fluctuating wildly, or it’s not working at all, the transmission speed sensor may be to blame.

Since the speed sensor provides data to the speedometer, a malfunctioning sensor might feed incorrect information or none at all, leading to these problems. Unstable or zero readings from your speedometer while driving are sure signs that you need to inspect the transmission speed sensor.

Loss of Power: Reduced Engine Performance and Power Output

Loss of power or a decrease in engine performance is another common symptom of a faulty speed sensor. The engine control unit (ECU) relies on the data from the speed sensor to control several aspects of the engine’s operation, including fuel mixture and ignition timing.

A malfunctioning sensor might send incorrect signals, causing the ECU to make inadequate adjustments. This situation could lead to a noticeable loss of power, particularly during acceleration, and reduced overall engine performance.

For more details on what happens when a speed sensor goes bad, you can visit this page.

Transmission Stalling: Failure of the Transmission to Engage or Sudden Stalls

Transmission stalling, or the sudden failure of the transmission to engage, is a more severe symptom of a bad speed sensor. This symptom could put the driver and passengers in danger, especially if it happens while driving.

If the transmission abruptly slips into neutral while the vehicle is in motion, it’s an urgent signal to inspect the transmission speed sensor.

Malfunction Indicator Light (MIL): Activation of the MIL or Check Engine Light

Lastly, if your Malfunction Indicator Light (MIL), commonly known as the check engine light, comes on, it could indicate a problem with the transmission speed sensor. Although the MIL can light up for various reasons, combined with other symptoms mentioned, it should prompt a check of the transmission speed sensor.

To understand the role of the check engine light and other indicators of a bad speed sensor, check out this link.

Causes of Transmission Speed Sensor Failure

Wear and Tear due to Mileage and Age

Just like any other mechanical component, a transmission speed sensor is subject to the natural process of wear and tear. Over time, and with the accumulation of mileage, the sensor’s efficiency may deteriorate. Particularly, in older vehicles, the age of the component can be a significant factor leading to its malfunction.

Exposure to Extreme Temperatures or Harsh Conditions

Transmission speed sensors can also go bad due to exposure to extreme temperatures or harsh driving conditions. Overheating is a common issue in transmissions that can extend to damage the transmission speed sensor. Simultaneously, sensors can also fail due to their exposure to cold temperatures, especially in regions with severe winters.

Moreover, driving in challenging conditions, such as off-road or on rough terrain, can result in physical damage to the sensor. This type of damage could result from debris or rough contact with the road surface, especially if the sensor is located in a vulnerable position.

Electrical Issues or Wiring Problems

Electrical problems are another significant cause of speed sensor failure. Wiring issues can result in an intermittent or permanent loss of electrical connectivity, causing the sensor to fail. Corroded connections, damaged wires, or loose connectors are common electrical problems that can lead to a malfunctioning speed sensor.

Fluid Contamination or Leaks

Fluid leaks in your transmission can also contribute to speed sensor failure. If the transmission fluid leaks and contaminates the sensor or its connecting circuitry, the sensor can provide inaccurate readings or fail altogether. Additionally, contaminated transmission fluid (with metal shavings or dirt) can also lead to sensor malfunction.

For more information on the causes of transmission speed sensor failure, you might find this article useful.

Diagnosing a Faulty Transmission Speed Sensor

Using Diagnostic Tools and Scanning for Trouble Codes

Modern vehicles come equipped with a computerized system that monitors and controls various vehicle operations, including the transmission. When a component like the transmission speed sensor fails, it typically triggers a trouble code that is stored in the vehicle’s computer system.

To access these trouble codes, you’ll need a diagnostic scan tool. This device can be connected to the vehicle through the Onboard Diagnostics II (OBD-II) port, typically located under the dashboard. Once connected, the tool can scan the vehicle’s computer system and retrieve any stored codes.

Specific codes are associated with potential transmission speed sensor problems. For instance, P0715 refers to an issue with the input speed sensor, while P0720 indicates a problem with the output speed sensor. These codes can help pinpoint the source of the problem, saving time and effort in troubleshooting.

Conducting Visual Inspections and Sensor Tests

While trouble codes can guide you towards potential issues, a visual inspection can provide additional confirmation. Examine the sensor and its connections for any visible signs of damage, corrosion, or disconnection. Also, check for any signs of fluid contamination, which could indicate leaks in the transmission.

In addition to visual inspection, you can test the sensor using a digital multimeter. By checking the sensor’s voltage readings while the engine is running, you can determine whether it’s working correctly. An abnormal reading could indicate a faulty sensor.

Seeking Professional Help for Accurate Diagnosis

While these steps can help identify a bad transmission speed sensor, diagnosing automotive issues can sometimes be complex, requiring professional knowledge and experience. If you’re unsure, it’s always best to seek help from a professional mechanic. They have specialized tools and knowledge to accurately diagnose and fix the problem.

Potential Consequences of Ignoring a Bad Speed Sensor

Increased Risk of Transmission Damage and Costly Repairs

Ignoring the symptoms of a bad transmission speed sensor can lead to significant consequences, including the risk of serious transmission damage. Without accurate input from the speed sensor, the vehicle’s computer cannot make the necessary adjustments to the engine’s operation and gear shifting. This lack of control can lead to overheating and excessive wear on the transmission, leading to costly repairs or even the need for a complete transmission rebuild.

For more information about the consequences of a bad speed sensor, you can visit this link.

Negative Impact on Fuel Efficiency and Overall Vehicle Performance

A faulty speed sensor can also negatively impact the vehicle’s fuel efficiency. The engine control unit relies on the speed sensor data to adjust the fuel-air mixture and ignition timing for optimal fuel efficiency. Incorrect data due to a faulty sensor can result in poor fuel economy.

Furthermore, the overall vehicle performance, including power output, gear shifting, and the accuracy of the speedometer, can be adversely affected.

The next section will guide you through the process of replacing a faulty transmission speed sensor.

How to Replace a Faulty Transmission Speed Sensor

Necessary Tools and Safety Precautions

Before starting the replacement process, ensure that you have the necessary tools, including a wrench set, jack stands, a new transmission speed sensor, and safety gear such as gloves and safety glasses.

Remember that working on your vehicle can pose safety risks. Always prioritize your safety by working on a flat, stable surface, and use jack stands when lifting your vehicle. If you’re unsure or uncomfortable performing the replacement yourself, it’s advisable to seek professional help.

Step-by-Step Guide for Removing the Old Sensor and Installing a New One

The exact process of replacing the transmission speed sensor may vary depending on the vehicle’s make and model, but the following steps provide a general guide:

  1. Locate the Transmission Speed Sensor: First, you’ll need to locate the transmission speed sensor on your vehicle. Typically, it is found on the transmission’s exterior and looks like a small plug with a connecting wire. Refer to your vehicle’s manual or look up the sensor’s location online if you have trouble finding it.
  2. Remove the Old Sensor: After locating the sensor, disconnect the wiring harness attached to it. Then, using your wrench, carefully unscrew and remove the faulty speed sensor from the transmission.
  3. Install the New Sensor: Next, install the new speed sensor. Screw it into the transmission using your wrench, but be careful not to over tighten as this could damage the new sensor. Once the sensor is securely in place, reconnect the wiring harness.
  4. Test the New Sensor: Start your vehicle and test drive it to ensure the new sensor is functioning correctly. Pay attention to the smoothness of gear shifts and the accuracy of the speedometer. If any problems persist, further diagnostics may be necessary.

For a more detailed explanation of how to replace a speed sensor, you can follow this guide.

Proper Sensor Calibration and Testing After Replacement

After replacing the transmission speed sensor, it’s crucial to ensure the sensor is properly calibrated and functioning as intended. You may need to use a diagnostic tool to reset the vehicle’s computer to recognize the new sensor.

Additionally, it would be best to take your vehicle for a test drive to monitor the transmission’s behavior. Pay close attention to the speedometer readings and gear shifts, as these should now operate smoothly. If any issues persist after replacing the sensor, seek professional help, as there might be other underlying issues.

Frequently Asked Questions (FAQs)

Can I drive with a bad transmission speed sensor?

While it’s technically possible to drive with a faulty transmission speed sensor, it is not recommended. The problems associated with a bad speed sensor, like erratic shifting and a malfunctioning speedometer, can make driving challenging and unsafe. Additionally, continuing to drive with a faulty speed sensor could potentially cause further damage to the transmission, leading to more costly repairs in the future.

How long does it take to replace a transmission speed sensor?

The process of replacing a transmission speed sensor can take anywhere from 30 minutes to a couple of hours, depending on the vehicle’s make and model and the sensor’s location. For vehicles where the sensor is easily accessible, the process could be relatively quick. However, for vehicles where the sensor is harder to reach, it may take longer.

Can a faulty speed sensor cause other transmission problems?

Yes, a faulty speed sensor can cause other transmission problems. The speed sensor provides crucial information to the vehicle’s computer system to control various transmission functions, including gear shifting. If this information is inaccurate or missing due to a faulty sensor, it can lead to issues like erratic shifting, overheating, and excessive wear on the transmission components.

How much does it cost to replace a transmission speed sensor?

The cost to replace a transmission speed sensor can vary widely based on the vehicle’s make and model, the cost of the part, and labor costs if you choose to have a professional do the job. On average, you can expect the part to cost between $50 to $300, and if you include professional installation, the total cost can range from $100 to $400.

Here are some external resources that might help you learn more about diagnosing and repairing transmission speed sensor issues.


The transmission speed sensor is a crucial component of your vehicle’s transmission system. It provides essential data that influences various vehicle operations, including gear shifting and the vehicle’s speedometer readings. A functioning transmission speed sensor ensures smooth shifting between gears, accurate speedometer readings, and optimal fuel efficiency.

When a speed sensor goes bad, you may encounter erratic shifting, inaccurate speedometer readings, or even find your vehicle stalling mid-drive. Not only can these symptoms make driving challenging and unsafe, but they can also lead to other problems. Ignoring these signs could potentially cause further damage to your transmission and lead to more costly repairs.

Recognizing the symptoms of a faulty speed sensor and diagnosing the problem accurately are the first steps towards resolution. Diagnostic tools and trouble codes can assist in identifying the issue, while visual inspections and sensor tests can provide further confirmation.

Replacing a faulty speed sensor might seem daunting, but with the right tools and instructions, it can be a manageable task. Remember, safety should be your priority when working on your vehicle. If you’re uncertain or uncomfortable performing the repair yourself, seeking help from a professional mechanic is recommended.

As we’ve covered in this article, dealing with a bad transmission speed sensor is not a situation to ignore. Regular maintenance and early detection are vital to prevent potential damage to your vehicle’s transmission system, ensuring your vehicle performs optimally and safely.

For more information about diagnosing and fixing speed sensor issues, you can visit this guide. Additionally, forums like this one can provide firsthand accounts and advice from others who have experienced similar problems.

Remember, understanding the importance of a properly functioning transmission speed sensor and acting promptly on any symptoms can save you from potential inconvenience, high repair costs, and even road safety hazards.


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