Causes and Repair Methods for Trouble Code P0720

In the realm of modern automobiles, the dashboard lights and diagnostic trouble codes (DTCs) serve as a direct line of communication between your vehicle and its driver. When the dreaded “check engine” light illuminates, it often sends a wave of anxiety through the hearts of car owners. One such code that frequently appears is P0720, indicating an Output Speed Sensor Circuit Malfunction. This article delves into the specifics of the P0720 code, what it means, its potential causes, and how to address it.

What is P0720?

P0720 is a Diagnostic Trouble Code (DTC) used in the world of automotive diagnostics. It specifically refers to a problem with the Output Speed Sensor (OSS) circuit, and it is a standardized code used across various vehicle makes and models. The P0720 code is a part of the On-Board Diagnostics II (OBD-II) system, which is present in most vehicles manufactured since the mid-1990s.

To understand P0720, let’s break it down:

• “P” stands for Powertrain. In the OBD-II system, “P” codes relate to issues within the powertrain, which encompasses the engine and transmission.
• “0” refers to the generic nature of the code. A “0” in this position means it’s a generic code that applies to all vehicle manufacturers.
• “720” is the specific code that signifies the problem with the Output Speed Sensor Circuit.

The Output Speed Sensor (OSS):

The Output Speed Sensor is a vital component in modern automatic transmissions. It plays a key role in monitoring the rotational speed of the output shaft, which is directly connected to the vehicle’s wheels. This sensor provides critical data to the vehicle’s Engine Control Module (ECM) or Transmission Control Module (TCM) for various functions, including:

1. Shift Timing: The ECM or TCM uses the information from the OSS to determine when to shift gears. This data helps ensure smooth and efficient transitions between gears.
2. Torque Converter Lock-Up: The OSS data is used to control the engagement and disengagement of the torque converter, which can significantly affect fuel efficiency and performance.
3. Cruise Control: The OSS is instrumental in maintaining a constant speed when using cruise control. It ensures that the vehicle maintains a steady pace.

Circuit Malfunction:

The term “circuit malfunction” in the context of the P0720 code implies that there is an issue within the electrical circuit related to the Output Speed Sensor. In other words, the sensor itself may be functioning correctly, but there’s a problem with the wires, connectors, or other electrical components that facilitate communication between the sensor and the ECM or TCM.

In essence, when your vehicle’s computer detects a P0720 code, it is indicating that there is a breakdown in communication between the Output Speed Sensor and the control module due to an issue within the circuit. This can have a cascading effect on the vehicle’s performance and functionality, including transmission behavior, shift patterns, and even fuel efficiency.

Symptoms of Code P0720

When your vehicle’s onboard computer detects a P0720 code, indicating an Output Speed Sensor Circuit Malfunction, it often manifests in various noticeable symptoms. Recognizing these symptoms is essential for diagnosing and addressing the issue promptly. Here are in-depth details about the symptoms of Code P0720:

1. Check Engine Light (CEL) Illumination: The most common and readily visible symptom of a P0720 code is the illumination of the Check Engine Light (CEL) on your vehicle’s dashboard. The Check Engine Light serves as an alert that the vehicle’s electronic control module (ECM) has detected a problem in the Output Speed Sensor Circuit. It’s important not to ignore this warning, as it can indicate a range of issues, including those related to the transmission.
2. Sluggish or Delayed Shifting: Another prevalent symptom of P0720 is sluggish or delayed shifting in the vehicle’s transmission. The Output Speed Sensor plays a crucial role in ensuring the smooth operation of the transmission system. When this sensor malfunctions, it can result in slower gear changes or delayed shifts. This can be particularly noticeable during acceleration and deceleration, causing a lack of responsiveness in your vehicle.
3. Unpredictable or Harsh Gear Changes: On the flip side, a P0720 code can lead to unpredictable or harsh gear changes. This symptom is often characterized by jarring transitions between gears, which can create a disconcerting and uncomfortable driving experience. It may also affect the overall drivability of the vehicle.
4. Poor Fuel Economy: A malfunctioning Output Speed Sensor Circuit can impact the fuel economy of your vehicle. When the transmission doesn’t shift gears as it should, it can result in reduced fuel efficiency. You may notice a decrease in miles per gallon (MPG), leading to higher fuel expenses over time. This symptom is particularly concerning in an era of increasing fuel costs and environmental awareness.
5. Stalling or Inconsistent Engine Performance: P0720 can have broader implications on the overall engine performance. Some drivers have reported instances of engine stalling or inconsistency in performance. The Output Speed Sensor’s malfunction can disrupt the balance between engine and transmission operations, causing problems during acceleration or deceleration. In severe cases, this can affect safety, especially in situations where reliable power delivery is necessary.
6. Diagnostic Trouble Codes (DTCs): In addition to the P0720 code itself, the ECM may store other diagnostic trouble codes (DTCs) in its memory. These codes can provide additional information about the specific issues affecting the Output Speed Sensor Circuit. Examining these codes can help in pinpointing the root cause of the problem.

Causes of P0720: Output Speed Sensor Circuit Malfunction

The P0720 code, which indicates an Output Speed Sensor Circuit Malfunction, can be triggered by a variety of underlying causes. Understanding these causes is crucial for effectively diagnosing and addressing the issue. Here are the in-depth details about the potential causes of P0720:

Wiring Issues:

Corroded Wiring: Over time, the wiring connecting the Output Speed Sensor (OSS) to the Engine Control Module (ECM) or Transmission Control Module (TCM) can deteriorate due to exposure to moisture, road salt, and other environmental factors. This corrosion can lead to interruptions in the electrical signal, causing the OSS circuit to malfunction.

Damaged Wiring: Physical damage to the wiring, such as cuts, abrasions, or fraying, can disrupt the flow of electrical signals. This can result from accidents, rodent damage, or simply wear and tear over time.

Loose or Poor Connections: Loose or poorly connected wiring, connectors, or terminals can also cause issues within the OSS circuit. Loose connections may not provide a stable electrical pathway, leading to signal loss.

Sensor Failure:

Wear and Tear: The Output Speed Sensor itself can degrade over time due to normal wear and tear. As the sensor’s components deteriorate, it may produce inaccurate or erratic readings, leading to the P0720 code.

Manufacturing Defects: In some cases, the Output Speed Sensor may have manufacturing defects that result in premature failure. These defects can include faulty internal components, wiring, or connectors.

Extreme Conditions: Harsh operating conditions, such as extreme temperatures or exposure to contaminants, can accelerate the wear and deterioration of the OSS, making it more prone to failure.

ECM Problems:

ECM Malfunctions: The Engine Control Module (ECM), also known as the Powertrain Control Module (PCM), is the central computer that controls various vehicle functions, including transmission operation. If the ECM itself is faulty or experiencing issues, it can disrupt communication with the Output Speed Sensor, leading to the P0720 code.

Software or Programming Errors: Sometimes, ECM-related problems can be attributed to software or programming errors. These errors can affect how the ECM interprets and utilizes data from the OSS, resulting in erroneous readings.

Transmission Issues:

Torque Converter Problems: The torque converter is a critical component within the transmission. If the torque converter is failing or malfunctioning, it can directly impact the speed of the output shaft, which the Output Speed Sensor monitors. Problems with the torque converter can trigger a P0720 code.

Mechanical Failures: Various mechanical issues within the transmission, such as damaged gears or bearings, can affect the rotational speed of the output shaft. These issues can lead to inaccurate OSS readings and, subsequently, the P0720 code.

Diagnosing P0720: Output Speed Sensor Circuit Malfunction

Diagnosing a P0720 code, which signifies an Output Speed Sensor Circuit Malfunction, is a critical step in resolving the issue and ensuring the proper functioning of your vehicle’s transmission system. Professional diagnosis is highly recommended to accurately pinpoint the root cause and apply the appropriate repairs. Here are in-depth details about the diagnostic process for P0720:

Code Scanning:

The diagnostic process for a P0720 code typically begins with the use of an On-Board Diagnostics II (OBD-II) scanner. This scanner is a standard tool used by mechanics and technicians to interface with your vehicle’s computer system. The steps involved in this phase include:

• Connecting the Scanner: The OBD-II scanner is connected to the vehicle’s diagnostic port, typically located beneath the dashboard near the steering column.
• Retrieving the Code: The scanner retrieves the specific diagnostic trouble code (DTC), in this case, P0720. It also provides additional information, such as freeze frame data, which can offer insight into the conditions under which the code was triggered.
• Recording the Code: The technician records the code for reference during the diagnosis and repair process.

Visual Inspection:

After retrieving the code, a visual inspection of the vehicle and its components is conducted. This step aims to identify any obvious issues that may be contributing to the P0720 code:

• Output Speed Sensor and Wiring Inspection: The mechanic inspects the Output Speed Sensor (OSS) and its associated wiring for visible damage, loose connections, or corrosion. Issues such as disconnected or damaged wiring can be readily identified during this inspection.

Circuit Testing:

Circuit testing is a crucial step to determine the integrity of the electrical pathway between the Output Speed Sensor and the Engine Control Module (ECM) or Transmission Control Module (TCM). Here’s how it’s done:

• Testing for Continuity: The technician uses a multimeter to check for continuity in the wiring. A lack of continuity could indicate a break or damage in the wires. Continuity tests are performed at various points along the circuit, including at the Output Speed Sensor and ECM/TCM connections.
• Voltage Testing: Voltage testing is conducted to ensure that the correct voltage is being supplied to the Output Speed Sensor. This test helps identify potential issues with the power supply to the sensor.

Sensor Testing:

If the wiring and circuitry check out as functioning correctly, the Output Speed Sensor itself may be tested to verify its operation:

• Sensor Output Testing: The technician uses an oscilloscope or multimeter to test the electrical output of the sensor as the vehicle’s wheels turn. The sensor should generate a consistent signal within the expected voltage range. Deviations from this range can indicate a faulty sensor.
• Resistance Testing: In some cases, the technician may measure the resistance of the Output Speed Sensor. A significant deviation from the specified resistance value can signal a problem with the sensor.

ECM Evaluation:

If no issues are detected with the wiring, circuitry, or the sensor itself, attention may turn to the ECM. This computer is responsible for processing the data from the Output Speed Sensor and controlling transmission functions. The steps involved in ECM evaluation include:

• Scan for ECM Errors: The technician may perform a comprehensive scan of the ECM to check for any errors or issues related to its operation.
• Software and Programming Check: Software-related issues or programming errors within the ECM can affect its interpretation of sensor data. The technician may update or reprogram the ECM to address such issues.

Transmission Inspection:

If all other components appear to be functioning correctly, the transmission itself may be examined for mechanical problems:

• Torque Converter Examination: The condition of the torque converter is assessed to determine if it’s functioning correctly. Mechanical issues in the torque converter can affect the output shaft speed, triggering a P0720 code.
• Transmission Inspection: Various mechanical components within the transmission, such as gears, bearings, and shafts, may be inspected for signs of wear, damage, or misalignment.

Repairing P0720: Output Speed Sensor Circuit Malfunction

Repairing a P0720 code, which signifies an Output Speed Sensor Circuit Malfunction, is essential for restoring your vehicle’s proper transmission operation and performance. The specific repair process will depend on the underlying cause of the code, which can vary from wiring issues to sensor failure or ECM problems. Here are in-depth details about the repair process for P0720:

Wiring Repair or Replacement:

If the diagnosis reveals that the issue is related to damaged or corroded wiring within the Output Speed Sensor (OSS) circuit, the following repair steps are typically undertaken:

• Locate the Faulty Wiring: Using the diagnostic information and visual inspection findings, the technician identifies the section of wiring that is compromised. This could be a specific wire or connector.
• Repairing Damaged Wiring: If the issue is limited to damage in a particular section of wiring, the technician may choose to repair it. This often involves cutting out the damaged portion and splicing in new wire, followed by proper insulation and protection.
• Replacing Severely Corroded Wiring: In cases where the wiring is severely corroded, it’s more practical to replace the entire length of the affected wire. This ensures a reliable and long-lasting repair.
• Weatherproofing: To prevent future issues with the wiring, technicians often apply weatherproofing measures, such as heat-shrink tubing or protective sleeves, to safeguard the repaired or replaced wiring against environmental factors.

Sensor Replacement:

If the Output Speed Sensor itself is found to be faulty, replacement is typically the most straightforward solution:

• Locate and Access the Sensor: The OSS is located on the transmission or transfer case. The technician locates the sensor, disconnects the wiring harness, and removes the sensor.
• Sensor Replacement: A new Output Speed Sensor is installed in place of the old, faulty one. Proper torque settings are used during installation to ensure the sensor is securely in place.
• Clearing the Code: Once the new sensor is in place, the technician uses the OBD-II scanner to clear the P0720 code from the vehicle’s computer memory.
• Test Drive: It’s common practice to conduct a test drive to ensure that the vehicle no longer exhibits the symptoms associated with the P0720 code. This ensures that the new sensor is functioning correctly.

ECM Replacement or Repair:

If the Engine Control Module (ECM) is identified as the source of the problem, the repair process can be more complex:

• Replacement: In some cases, replacing the ECM may be the most practical solution. The new ECM is programmed to match the vehicle’s specifications, and it may require additional programming to integrate it properly.
• Repair: Depending on the nature of the ECM issue, it might be repairable. Some common ECM issues, like faulty solder joints or damaged components, can be repaired by specialists. However, not all ECM issues are repairable, and a replacement might still be necessary.
• Software Updates: In cases where the ECM issue is related to software or programming errors, the technician may update or reprogram the ECM with the latest software from the vehicle manufacturer to address the issue.

Transmission Repair:

When the root cause of the P0720 code is mechanical problems within the transmission, more extensive repair work is often needed:

• Transmission Inspection: A thorough examination of the transmission components is performed to identify the specific issue, such as damaged gears, worn bearings, or other mechanical failures.
• Component Replacement: Depending on the findings, the technician may replace or repair damaged transmission components. This can include gears, bearings, or the torque converter, depending on the issue.
• Transmission Reassembly: Once the necessary repairs are complete, the transmission is reassembled, and all components are properly torqued to manufacturer specifications.
• Test and Calibration: The transmission is tested, and adjustments are made to ensure it functions correctly. This may include calibration of sensors and testing of gear shifts.

Preventing P0720: Output Speed Sensor Circuit Malfunction

Preventing a P0720 code, which indicates an Output Speed Sensor Circuit Malfunction, is a proactive approach to maintaining the reliability and performance of your vehicle’s transmission system. While you can’t entirely eliminate the risk of encountering this issue, several preventive measures can significantly reduce the likelihood of a P0720 code occurring. Here are in-depth details about how to prevent P0720:

Regular Maintenance:

Routine maintenance is one of the most effective ways to prevent P0720 and other transmission-related issues. Here’s what you should focus on:

• Transmission Fluid Changes: Regularly change the transmission fluid at intervals recommended by the vehicle manufacturer. Fresh transmission fluid helps maintain proper lubrication and cooling, reducing wear on transmission components and sensors.
• Filter Replacement: When changing the transmission fluid, replace the transmission filter. A clogged or dirty filter can restrict fluid flow and lead to issues with sensor readings.
• Scheduled Inspections: Include transmission system inspections in your vehicle’s regular maintenance schedule. During these inspections, a qualified mechanic can check for signs of wear, damage, or emerging issues with the Output Speed Sensor and its circuit.
• Computer Diagnostics: Use diagnostic equipment to check for any stored trouble codes, even if the check engine light is not illuminated. Addressing any pending or potential issues before they become critical can prevent P0720.

Protecting Wiring:

As a significant cause of P0720 is damaged or corroded wiring, taking steps to protect the wiring associated with the Output Speed Sensor is essential:

• Insulation: Ensure that the wiring is properly insulated, protecting it from exposure to the elements and potential abrasion. Insulation can prevent moisture and debris from affecting the wiring.
• Weatherproofing: Use weatherproofing measures, such as heat-shrink tubing or protective sleeves, to safeguard the wiring against environmental factors. This can help prolong the life of the wiring and reduce the risk of corrosion.
• Routing: Properly route and secure the wiring to prevent it from chafing or becoming entangled with other components. Avoid sharp edges and hot surfaces that can damage the wiring over time.

Quality Parts:

When replacement of the Output Speed Sensor or its components is necessary, prioritize high-quality and reliable parts:

• OEM Parts: Whenever possible, opt for Original Equipment Manufacturer (OEM) parts. These parts are specifically designed for your vehicle’s make and model, ensuring a proper fit and performance.
• Aftermarket Parts: If you choose aftermarket parts, select reputable brands and ensure they meet or exceed the manufacturer’s specifications. Inexpensive or subpar parts can lead to premature sensor failure.
• Professional Installation: Have parts professionally installed to ensure they are properly integrated into your vehicle. Professional technicians have the expertise to carry out correct installations, which can prevent issues that lead to P0720.

Avoiding Extreme Conditions:

Extreme conditions, such as extreme temperatures, heavy off-road use, and deep water crossings, can accelerate wear and tear on vehicle components, including the Output Speed Sensor. To prevent P0720:

• Drive Carefully: Avoid rough or abusive driving that can cause stress on the transmission and its components.
• Off-Roading: If you engage in off-road activities, choose appropriate vehicles and equipment designed for such conditions to reduce wear on the transmission.
• Maintain Proper Fluid Levels: Ensure that transmission fluid is maintained at the correct level, especially if you drive in extreme temperatures. Low fluid levels can lead to overheating and increased wear on the transmission.

A P0720 code, indicating an Output Speed Sensor Circuit Malfunction, can affect the performance and efficiency of your vehicle. While it may not be an immediate emergency, prompt attention and repair are essential to prevent further damage and ensure safety on the road. By following proper diagnostic procedures and taking preventive measures, you can keep your vehicle running smoothly and avoid the reoccurrence of the P0720 code in the future.