The P0720 diagnostic trouble code (DTC) indicates a problem with the Output Shaft Speed (OSS) sensor circuit in your Ford vehicle. This sensor plays a crucial role in determining shift scheduling, torque converter engagement, and electronic pressure control within the transmission. Understanding this code and its potential causes can help you diagnose and address the issue effectively.
What Does the P0720 Code Mean?
In electronically controlled transmissions, the OSS sensor monitors the output shaft’s speed. This data is sent to the Powertrain Control Module (PCM) or Engine Control Module (ECM), which uses it to manage various transmission functions. When the PCM/ECM detects a malfunction in the OSS sensor circuit, it triggers the P0720 code. The PCM/ECM might try to compensate for the missing OSS data by using information from other sensors, but this can lead to performance issues. The OSS sensor is also commonly used to provide vehicle speed information to the speedometer.
Symptoms of a P0720 Code in a Ford
A P0720 code can manifest in several ways, including:
- Delayed or erratic shifting: The transmission may struggle to shift gears smoothly or at the correct time.
- Malfunctioning speedometer: The speedometer may provide inaccurate readings or stop working altogether.
- Illuminated Check Engine Light: The check engine light on your dashboard will turn on, indicating a problem with the powertrain.
- Reduced fuel economy: In some cases, a faulty OSS sensor can negatively impact fuel efficiency.
- Limp mode: The vehicle might enter a “limp mode” to prevent further damage, limiting speed and performance.
Common Causes of a P0720 Code
Several factors can contribute to a P0720 code in a Ford:
- Faulty Output Shaft Speed Sensor: The OSS sensor itself may be damaged or worn out, causing inaccurate readings or no signal at all.
- Wiring or Connector Issues: Damaged wiring, corroded connectors, or loose connections in the OSS sensor circuit can disrupt the signal transmission.
- Transmission Fluid Temperature (TFT) Sensor Problems: In some Ford models, the OSS sensor is linked to the TFT sensor. A malfunctioning TFT sensor or its wiring can affect the OSS sensor’s performance. This is because a common ground is shared between the two components.
- Damaged Tone Ring: The tone ring, a toothed wheel that the OSS sensor uses to detect speed, can be damaged, leading to incorrect readings. This is less common than sensor failure.
- Low Transmission Fluid: Although less directly related, low transmission fluid can cause erratic sensor readings. Always check your fluid level.
Diagnosing and Repairing a P0720 Code
Diagnosing a P0720 code typically involves the following steps:
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Visual Inspection: Inspect the OSS sensor, wiring harness, and connectors for any visible damage, corrosion, or loose connections. Pay close attention to areas where the harness may rub against other components.
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Sensor Testing: Use a multimeter or oscilloscope to test the OSS sensor’s resistance and signal output. Compare your readings to the manufacturer’s specifications.
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Wiring Harness Testing: Check for continuity and resistance in the wiring harness between the OSS sensor and the PCM/ECM.
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TFT Sensor Testing (if applicable): If your Ford model uses a combined OSS/TFT sensor, test the TFT sensor’s resistance and signal.
Conclusion
The P0720 code signifies a problem with the OSS sensor circuit, which can significantly impact your Ford’s transmission performance and drivability. Addressing this issue promptly is crucial to prevent further damage and ensure safe operation. By understanding the symptoms, causes, and diagnostic procedures, you can effectively troubleshoot and resolve the P0720 code in your Ford. If you are not comfortable performing these diagnostic steps yourself, consult a qualified mechanic for assistance.
