P0722 - Output Speed Sensor Circuit Low Input

Introduction

The P0722 diagnostic trouble code (DTC) indicates a problem with the output speed sensor (OSS) circuit in your vehicle. The OSS is a crucial component of the transmission system, responsible for monitoring the rotational speed of the transmission's output shaft. This information is used by the powertrain control module (PCM) or transmission control module (TCM) to manage shift timing, torque converter lockup, and other essential transmission functions. When the PCM/TCM detects a low voltage or signal frequency from the OSS circuit, it triggers the P0722 code, potentially leading to transmission performance issues. Addressing this code promptly is crucial to prevent further damage and ensure smooth vehicle operation.

Comprehensive Table: P0722 - Output Speed Sensor Circuit Low Input

Detailed Explanations

Sensor Function: The Output Speed Sensor (OSS) is a crucial component that monitors the rotational speed of the transmission's output shaft. This information is relayed to the PCM/TCM, allowing the vehicle to accurately manage shift points, torque converter lockup, and other critical transmission functions. A properly functioning OSS ensures smooth and efficient operation of the transmission system. In some vehicle models, the OSS data is also used by the Anti-lock Braking System (ABS) and Traction Control System (TCS) to determine wheel slip and adjust braking or engine power accordingly.

Code Definition: The P0722 code, "Output Speed Sensor Circuit Low Input," is triggered when the PCM/TCM detects that the voltage or signal frequency coming from the OSS circuit is below the expected threshold. This signifies that the signal is either absent or significantly weaker than anticipated. The PCM/TCM relies on a consistent and accurate signal from the OSS to properly control transmission functions. A low input signal indicates a problem within the OSS circuit that needs to be diagnosed and resolved.

Symptoms: The symptoms of a P0722 code can vary, but commonly include harsh or erratic shifting, where the transmission shifts roughly or at unexpected times. Transmission slipping, where the transmission fails to properly engage gears, is another frequent symptom. Torque converter lockup problems, resulting in reduced fuel efficiency, can also occur. The check engine light will illuminate on the dashboard, alerting the driver to the issue. In some cases, the vehicle may enter limp mode, a reduced power mode designed to protect the transmission. Speedometer malfunction, inaccurate readings or complete failure, can also be a symptom. Finally, if the OSS signal is used by the ABS or TCS, these systems may also malfunction.

Possible Causes: A faulty Output Speed Sensor (OSS) is a common cause, as the sensor itself may be defective and unable to generate a proper signal. Wiring issues, such as damaged, corroded, or loose wiring or connectors in the OSS circuit, can also lead to the code. A short to ground in the OSS signal wire can cause a low voltage reading, triggering the P0722 code. Conversely, an open circuit, a break in the OSS signal wire, can prevent the signal from reaching the PCM/TCM. In rare cases, a PCM/TCM failure can cause it to misinterpret or fail to read the OSS signal. Internal transmission problems, such as a damaged reluctor wheel (tone ring) that the OSS reads, can affect the sensor's ability to generate an accurate signal. Low battery voltage can sometimes cause erratic sensor readings, while incorrect sensor installation, if the sensor was recently replaced, can also contribute to the problem.

Diagnostic Steps: The diagnostic process begins with reading and clearing the DTCs using a scan tool. Next, a visual inspection of the wiring and connectors associated with the OSS is crucial, looking for damage, corrosion, or looseness. The OSS resistance should be tested using a multimeter and compared to the manufacturer's specifications. The OSS signal voltage should be checked using a multimeter or oscilloscope while the vehicle is running or the wheels are turning. Inspecting the reluctor wheel (tone ring) for damage or debris is also important. Use a multimeter to check for shorts to ground or open circuits in the OSS wiring. Ensure the battery voltage is within the normal operating range. Performing a wiggle test, wiggling the wiring harness connected to the OSS while the engine is running, can help identify intermittent issues. Finally, consult a vehicle-specific wiring diagram to ensure proper connections and identify potential problem areas.

Tools Required: An OBD-II scan tool is essential for reading and clearing diagnostic trouble codes. A multimeter is needed to test voltage, resistance, and continuity in the OSS circuit. An oscilloscope is optional but can be helpful for visualizing the OSS signal waveform. A wiring diagram is crucial for identifying the correct wiring and connections. Basic hand tools, such as screwdrivers, pliers, and wire strippers, are also necessary. Jack and jack stands may be needed to safely access the OSS, and contact cleaner can be used to clean corroded connectors.

Related Codes: Several other DTCs are related to the P0722 code. P0720, "Output Speed Sensor Circuit," indicates a general circuit fault. P0721, "Output Speed Sensor Range/Performance," signifies that the OSS signal is out of the expected range. P0723, "Output Speed Sensor Circuit Intermittent," indicates an intermittent signal from the OSS. P0725, "Engine Speed Input Circuit," is related to engine speed, which can sometimes influence transmission behavior.

Severity: The severity of a P0722 code is moderate to high. While the vehicle may still be drivable, the transmission's performance will be compromised, potentially leading to further damage and safety concerns. Addressing the issue promptly is recommended to prevent further complications.

Repair Costs: Repair costs can vary significantly depending on the cause. Replacing the OSS typically costs between $50 and $200, including parts and labor. Wiring repair can range from $100 to $300 in labor costs. PCM/TCM replacement can be more expensive, ranging from $500 to $1500, including parts and labor. Transmission repair can be the most costly, ranging from $500 to $3000 or more, depending on the extent of the damage. These are estimated costs and can vary significantly based on the vehicle make, model, and location.

Frequently Asked Questions

• What does the P0722 code mean? The P0722 code indicates a low input signal from the output speed sensor circuit, signaling a problem with the sensor, wiring, or related components.

• Can I drive my car with a P0722 code? While you can drive with a P0722 code, it's not recommended, as the transmission may not shift properly, potentially leading to further damage.

• Is the output speed sensor the same as the vehicle speed sensor? In some vehicles, yes, the OSS and VSS are the same sensor; however, in others, they are separate components, each monitoring different aspects of vehicle speed.

• How do I fix a P0722 code? Fixing a P0722 code involves diagnosing the cause (sensor, wiring, etc.) and then repairing or replacing the faulty component.

• What are the symptoms of a bad output speed sensor? Common symptoms include harsh shifting, transmission slipping, speedometer malfunction, and the check engine light illuminating.

Conclusion

The P0722 code signals a problem with the output speed sensor circuit, potentially affecting transmission performance and vehicle safety. Prompt diagnosis and repair are crucial to prevent further damage and ensure smooth vehicle operation.