P0720 - OBD II Trouble Code

Auto Systems and Repair

Output Speed Sensor Circuit Malfunction

Our emissions expert has put together the following information about the P0720 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.

OBD II Fault Code

  • OBD II P0720

Fault Code Definition

  • Output Speed Sensor Circuit Malfunction
What does this mean?
When the code P0720 is set in the Powertrain Computer, it means that the Powertrain Computer or PCM is not seeing a rational speed signal from the Output Sensor or, there is a greater than specified RPM difference between the rotational speed of the Input RPM Sensor and the Transmission Output Speed RPM Sensor. This can occur during shifting or when driving at steady speeds in the same gear. It often implies that the transmission is slipping.

Want to Learn More?
The purpose of the automatic transmission is to match the engine's optimum power and torque characteristics to the driver's desired rate of acceleration and speed by auto-selecting different gear ratios or 'speeds' to power the wheels. 

Symptoms

  • Check Engine Light will illuminate
  • Vehicle will not shift properly
  • Decrease in fuel economy
  • In unusual cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be performance problems, such as dying when coming to a stop after driving on the freeway and/or misfire-like symptoms

Common Problems That Trigger the P0720 Code

  • Defective Output Speed Sensor
  • Defective Shift Solenoids
  • Defective Engine Coolant Temperature Sensor
  • Defective Valve Body
  • Dirty transmission fluid that restricts the hydraulic passages
  • Defective Output Speed Sensor wiring or connector

Common Misdiagnoses

  • Engine Misfire problem
  • Internal Transmission problem
  • Driveline problem

Polluting Gases Expelled

  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
  • CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
  • NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog

P0720 Diagnostic Theory for Shops and Technicians

When diagnosing a P0720  code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive. Pay close attention to the Output Speed Sensor vs engine load, throttle position, RPM, and road speed because a P0720 can be difficult to detect. If the signal is erratic or the values don't seem to make sense, then you may have verified the problem. 

 

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