Transmission

P0720 — Transmission Output Speed Sensor Circuit Fault

Severity: medium Drive with care, to a shop

What P0720 means

The output speed sensor reads how fast the transmission output shaft turns. The control module uses this to time shifts, manage hydraulic pressure and calculate vehicle speed. P0720 sets when the signal is missing, erratic or disagrees with other speed inputs.

Symptoms

  • Check Engine light on
  • Harsh, delayed or erratic shifts
  • Speedometer inaccurate or not working
  • Cruise control not working
  • Worse fuel economy
  • Engine flare during shifts
  • Transmission limp mode
  • ABS light on some cars that share the speed signal

Possible causes

  1. Failed output speed sensor
  2. Damaged, corroded or loose sensor wiring or connector
  3. Metal debris on the sensor tip
  4. Low or contaminated transmission fluid
  5. Open circuit or short to ground in the harness
  6. Faulty vehicle speed sensor (VSS)
  7. Rarely, a faulty transmission control module (TCM) or PCM

How to diagnose

  1. Scan all modules and note freeze frame data, including ABS or other speed sensor codes
  2. Compare scan tool vehicle speed with the speedometer and wheel speeds
  3. Check transmission fluid level and condition, looking for debris or burnt smell
  4. Inspect the sensor, connector and harness for chafing, oil, corrosion and poor contact
  5. Remove the sensor and check the tip for buildup or metal particles
  6. Test sensor resistance and the supply and signal circuits per the factory wiring diagram
  7. Check the harness for opens and shorts to ground back to the module
  8. Suspect the TCM or PCM only after everything else tests good

Common fixes

  • Replace the output speed sensor
  • Repair or replace damaged wiring and connectors
  • Change contaminated fluid and filter, and clean debris from the sensor
  • Reprogram or replace the TCM/PCM if confirmed faulty

P0720 on different brands

Ford · manuals
On Ford, P0720:14 means the output speed sensor circuit is open or shorted to ground; it describes the condition the monitor detected, not a confirmed failed part.

Questions and answers

Can I drive with a P0720 code?

Briefly and carefully, yes, but the transmission may shift hard or go into limp mode. The longer you drive, the greater the risk of transmission damage, so don't put off diagnosis.

Why did my speedometer stop working with P0720?

The output speed sensor signal is often used to calculate vehicle speed. If it drops out, the speedometer and cruise control may stop working.

What most often causes P0720?

Most often it is the sensor itself or its wiring and connector. Also check fluid level and cleanliness, since metal debris on the sensor can distort the signal.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.