P0720: Output Speed Sensor Circuit

What does P0720 mean?

The output speed sensor reports how fast the transmission output shaft turns. The control module uses it with the input speed to manage shifts, and on many vehicles it also feeds vehicle speed. When the signal is missing or implausible, it stores P0720.

Both references list the sensor and wiring as common causes, along with shift solenoids and fluid problems.

Common symptoms

• Check engine light on
• Erratic or harsh shifting
• Speedometer not working on some vehicles
• Transmission stuck in one gear

Common causes

The causes below are the ones commonly seen with P0720. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• A faulty output speed sensor
• Damaged wiring or a poor connector
• Faulty shift solenoids
• Low or dirty transmission fluid

What to check with a scanner

• Read all codes, including any transmission codes. Some vehicles store extra transmission codes that only a brand profile or dealer tool can see.
• Read freeze frame data for vehicle speed, rpm and temperature when the code set.
• In Live data, watch vehicle speed, engine rpm and, if your car reports it, transmission temperature while driving.
• Check the transmission fluid level and condition if your vehicle has a dipstick or check plug, following the owner's manual.

How to read and clear P0720 with OBD Master Pro

1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0720 is listed and note any other codes, since they often explain the cause.
5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0720 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0720.

When to see a mechanic

Get professional help if any of these apply:

• The transmission slips, will not shift or is stuck in one gear
• Shifts are harsh or the car moves poorly
• The fluid is low, burnt or leaking
• Several transmission codes appear together

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

Related trouble codes

See all OBD2 trouble code guides

Related guides

Check engine light on: what to do · How to read an OBD2 code (P, B, C, U) · Stored, pending and permanent codes and freeze frame · OBD2 readiness monitors explained · OBD2 glossary · OBD2 by car brand