P0720 indicates the Powertrain Control Module (PCM) has lost or abnormal signal from the Output Shaft Speed Sensor (OSS), also called the Vehicle Speed Sensor (VSS). This sensor monitors transmission output shaft RPM, which is critical for proper transmission shifting, speedometer operation, and vehicle stability systems.
The sensor itself has failed, either due to internal electrical failure or contamination from metal debris in transmission fluid.
Corroded, broken, or shorted wiring in the sensor circuit, often due to age, heat, or chafing against other components.
The tone ring (pulse wheel) on the output shaft has missing, damaged, or contaminated teeth, preventing accurate speed detection.
The sensor is not properly seated, is damaged, or the mounting surface is contaminated, causing intermittent signal.
Metal particles or debris on the sensor tip can interfere with the magnetic or Hall-effect signal generation.
The PCM itself has failed or has an internal circuit problem affecting speed sensor input processing.
The vehicle can typically be driven, but expect malfunctioning speedometer, potentially harsh transmission shifting, and inoperative cruise control. Some safety systems may also be affected.
This sometimes happens due to misdiagnosis or when other obvious causes have been ruled out. However, PCM failure is very rare for this code—the sensor, wiring, or tone ring is the cause in the overwhelming majority of cases.
On most vehicles, the OSS sensor is accessible and can be replaced with basic tools. Some may require transmission fluid draining or special procedures—consult a repair manual for your specific vehicle.
No. The code will remain stored until the underlying issue is properly diagnosed and repaired. Clearing codes without fixing the problem will result in the light returning.