The P0720 diagnostic trouble code (DTC) indicates a problem with the Output Speed Sensor (OSS) circuit. This generic powertrain code applies to OBD-II equipped vehicles, impacting various makes and models. This article will delve into the intricacies of the P0720 code, outlining its meaning, symptoms, potential causes, and diagnostic steps.
What Does the P0720 Code Mean?
In vehicles with electronically controlled transmissions, the OSS is crucial for monitoring the output shaft’s rotational speed. Located at the transmission’s tail end, before the driveshaft or drive axles, the OSS relays data to the Powertrain Control Module (PCM) or Engine Control Module (ECM). This information is vital for:
- Shift Scheduling: Determining optimal gear shifting points.
- Torque Converter Engagement: Managing the torque converter’s lock-up clutch.
- Electronic Pressure Control (EPC): Regulating transmission fluid pressure.
- Speedometer Function: Providing accurate vehicle speed readings.
A P0720 code signifies that the PCM/ECM has detected a malfunction within the OSS circuit. While the system might compensate using data from other sensors, this can lead to performance issues. Notably, a faulty Transmission Fluid Temperature (TFT) sensor, often located in proximity to the OSS, can also trigger this code due to shared wiring. If a TFT-related code accompanies P0720, investigate both sensors and their connecting wiring. This code shares similarities with P0721, P0722, and P0723, which also relate to output speed sensor issues.
Recognizing the Symptoms of a P0720 Code
A P0720 code can manifest in various driving symptoms:
- Delayed or Erratic Shifting: The transmission might hesitate or shift harshly.
- Malfunctioning Speedometer: Inaccurate or non-functional speed readings.
- Illuminated Check Engine Light: The MIL (Malfunction Indicator Lamp) will activate.
Pinpointing the Potential Causes of a P0720 Code
Several factors can contribute to a P0720 code:
- Faulty Output Shaft Speed Sensor: Damage to the sensor itself is a common culprit.
- Wiring or Connection Issues: Damaged, corroded, or loose wiring and connectors can disrupt the signal.
- Malfunctioning Transmission Fluid Temperature Sensor: As mentioned, a faulty TFT sensor can indirectly affect the OSS circuit.
Diagnosing and Repairing a P0720 Code
1. Inspecting the Output Shaft Speed Sensor:
- Visual Inspection: Examine the sensor for physical damage, especially if it uses a plastic gear. Replace if necessary.
- Resistance Test: Disconnect the sensor and use a Digital Volt Ohm Meter (DVOM) to measure resistance between terminals. Compare the reading to manufacturer specifications. Replace the sensor if the resistance is out of range.
- Power and Signal Check: Verify power supply to the sensor and monitor the signal using a DVOM or oscilloscope. Look for voltage drops or irregularities while the vehicle is in motion. If the OSS is inline with the TFT sensor, fluctuating voltage based on transmission fluid temperature is normal.
2. Examining the Electrical Wiring:
- Visual Inspection: Thoroughly inspect the wiring harness for damage, loose connections, or corrosion.
- Continuity Test: Use a DVOM to check for continuity and excessive resistance in the wiring between the sensor, TFT sensor (if applicable), and the PCM/ECM.
- Short Circuit Test: Test for shorts to ground and power using the DVOM.
3. Testing the Transmission Fluid Temperature Sensor (if applicable):
- Resistance Test: Disconnect the transmission wiring harness and measure the TFT sensor’s resistance using a DVOM. Compare with manufacturer specifications.
- Short Circuit Test: Check for shorts to ground within the TFT sensor circuit.
- Power Supply Check: Verify the PCM/ECM is providing the correct voltage to the TFT sensor.
Conclusion
Addressing a P0720 code requires a systematic approach. By carefully inspecting the OSS, wiring, and TFT sensor (if equipped), you can effectively diagnose the root cause and implement the necessary repairs. Remember to consult your vehicle’s specific repair manual for detailed procedures and specifications. This comprehensive troubleshooting guide empowers you to understand and resolve the Eobd/obdii Error P0720 effectively.
