Error code P0720 is defined as Output Speed Sensor Circuit Malfunction, which means there’s a problem with the output speed sensor circuit, causing performance issues in the vehicle such as hesitation when accelerating, engine stalling, and misfiring.

This error code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

Definition

Error code P0720 happens when the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) detects a problem in the vehicle’s output speed sensor circuit. The PCM depends on the signal from the output speed sensor, which it uses to determine the right shift strategy and send then that information to the transmission. If the PCM failed to receive information from the output speed sensor, or the information is erratic, sporadic, or simply not in a slow and steady increase, then it will trigger the error code P0720.

Common Symptoms

As with other error codes, Error Code P0720 activates the Check Engine light and registers the code to the vehicle’s memory system. Other symptoms include issues on the engine and transmission, such as:

  • Erratic or malfunctioning speedometer
  • Inability to shift or harsh shifting
  • Hesitation on acceleration
  • Misfiring engine
  • Stalling
  • Increase in fuel consumption

Possible Causes

Multiple factors can result in this error code, including:

  • Defective output speed sensor
  • Defective input speed sensor
  • Damaged or corroded wires or loose connectors
  • Defective engine drivability sensors
  • Contaminated, dirty, or low transmission fluid
  • Malfunctioning shift solenoids
  • Defective PCM (rare)

How to Check

Technicians diagnose this code using a generic OBD-II trouble code scanner, and usually start by examining the free frame data from the trouble code scanner, which provides the information about the code and allow them to search for additional detected trouble codes.

They will then reset the codes, restart the vehicle, and then take the vehicle for a test drive. If the code doesn’t come back, then the issue is intermittent, which means the problem is not in the output speed sensor.

If the code comes back, however, then the technician will proceed on further diagnosis by checking any basic issues that may have triggered the code, such as damages in the connectors or wires, and dirty, contaminated, or low transmission fluid. Any issues found must be addressed as soon as possible to resolve the problem. Of course, the codes should be reset to check if they come back.

If the code persists, then technicians will test the ground for the output speed sensor signal and reference voltage. If either circuit is open, they must be replaced.

How to Fix

Repairs for this code are pretty easy, but of course, they require proper diagnosis. Common repairs include:

  • Replacement of output speed sensor
  • Replacement of input speed sensor
  • Replacement of connectors or wires
  • Drain and refill of transmission fluid
  • Replacement of PCM

In most cases, Error Code P0720 will not keep the vehicle from being driven. However, the effects could get worse and worse if not repaired as soon as possible, which can cause further damage to the transmission.