The Obdii P0720 code signifies a problem with your vehicle’s Output Speed (OSS) sensor circuit. This sensor plays a crucial role in monitoring the transmission’s output shaft speed, providing data to the Powertrain Control Module (PCM) or Engine Control Module (ECM). This information is vital for proper shifting, torque converter engagement, and electronic pressure control within the transmission. When the P0720 code is triggered, it indicates a malfunction within the OSS sensor circuit.
How the OSS Sensor Works and Why it Matters
In modern vehicles with electronically controlled transmissions, the OSS sensor, typically located at the transmission’s tail end, monitors the output shaft’s rotational speed. It does this by generating a voltage signal that changes in frequency proportional to the shaft’s speed. This signal informs the PCM/ECM about the vehicle’s speed and the transmission’s output speed. This data allows the system to optimize shift timing, manage torque converter lockup, and regulate internal transmission pressure. A malfunctioning OSS sensor can disrupt these critical functions, leading to drivability issues. Additionally, the OSS sensor often contributes to speedometer readings.
Recognizing the Symptoms of a P0720 Code
A faulty OSS sensor circuit can manifest in several ways, including:
- Delayed or Erratic Shifting: The transmission may struggle to shift gears smoothly or at the correct time.
- Inaccurate or Non-Functional Speedometer: The speedometer may provide incorrect readings or cease to function altogether.
- Illuminated Check Engine Light: The “Check Engine” light on your dashboard will illuminate, signaling a diagnostic trouble code has been stored.
- Reduced Fuel Efficiency: In some cases, a malfunctioning OSS sensor can negatively impact fuel economy.
Diagnosing the Root Cause of the P0720 Code
Several potential culprits can trigger the P0720 code:
- Faulty OSS Sensor: The sensor itself may be damaged or worn out, failing to generate accurate signals.
- Wiring Issues: Damaged, corroded, or loose wiring within the OSS sensor circuit can disrupt signal transmission.
- Transmission Fluid Temperature (TFT) Sensor Problems: In some vehicles, the OSS sensor is integrated with the TFT sensor. A faulty TFT sensor or its wiring can impact the OSS sensor’s operation.
- Damaged Sensor Gear: Some OSS sensors utilize a plastic gear. Damage to this gear can prevent accurate speed readings.
Troubleshooting and Repairing the P0720 Issue
Addressing the P0720 code involves a systematic diagnostic approach:
- Visual Inspection: Begin by visually inspecting the OSS sensor, its wiring, and connectors for any obvious damage, corrosion, or loose connections.
- Sensor Testing: Use a multimeter to test the OSS sensor’s resistance and compare it to manufacturer specifications. An out-of-range reading often indicates a faulty sensor.
- Wiring Harness Check: Inspect the wiring harness for continuity and shorts using a multimeter. Refer to a wiring diagram for your specific vehicle model.
- TFT Sensor Inspection (if applicable): If your vehicle has an integrated TFT/OSS sensor, test the TFT sensor’s resistance and wiring.
- Advanced Diagnostics: If the basic checks don’t reveal the problem, more advanced diagnostic tools, such as a scan tool or oscilloscope, may be necessary to analyze the sensor’s signal pattern.
Conclusion
The OBDII P0720 code indicates a problem with the Output Speed Sensor circuit. While this issue can cause various drivability problems, a systematic diagnostic approach can pinpoint the root cause and lead to effective repairs. If you are not comfortable performing these diagnostics yourself, consult a qualified automotive technician.
