P0720 – Output shaft speed (OSS) sensor -circuit malfunction

By John Kershaw (Contact Me)
Last Updated 2016-01-17
Ed.D, PhD Philosophy, BSME

What Does Code P0720 Mean?

The TCM (transmission control module) or PCM (powertrain control module) has received an input signal from the transmission OSS (output speed sensor) or VSS (Vehicle speed sensor) that is erratic. Without a accurate output speed signal the transmission cannot properly shift the transmission or transaxle, so this code sets. Output speed sensors detect speed by using the revolution of the output gear which is also the parking pawl gear, which is used as a reluctor (valley) for either PM generator or a Hall-Effect sensor that creates a sine or square wave pulse signal. The pulse signal is sent to the control module (TCM or PCM) which processes it as the vehicle speed.

NOTE: Whenever diagnosing a 700 series DTC (Diagnostic Trouble Code) with a transmission, transfer case or other driveline components, check for a DTC under chassis and body systems, not just under “P” or powertrain/engine or emission control type codes. Module communications DTCs are “U” codes. These are most often found when looking for DTCs under chassis or body systems. Chassis related codes are labeled “C” and body system related codes are labeled “B” codes and these can cause drivetrain issues if they affect a sensor that is also used by the heating and air conditioning system.

What are the common causes of code P0720 ?

• Defective OSS (Output Speed Sensor) or VSS (Vehicle Speed Sensor)
• Wiring from control module (TCM or PCM) is open or shorted
• Defective or corroded electrical connectors

What are the symptoms of code P0720 ?

• MIL (Malfunction Indicator Lamp [Check Engine & Service Engine Soon])lights on
• Speedometer problems not displaying the right vehicle speed
• Shifting problems, either rough or no upshift
• Poor fuel economy
• Stalling in rare cases
• ISS (input speed sensor) DTC P0715 may also set

Codes Related to P0720

• DTC P0715, P1870.