P0720 means Output Speed Sensor Circuit. The computer is not getting a valid signal from the transmission output speed sensor, which measures driveshaft speed. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0720 means
Electronically controlled automatics are run by a transmission control module (TCM), a separate box or part of the engine computer. It reads speed sensors, the range sensor and fluid temperature to decide when to shift, and drives solenoids that apply clutches and the torque converter clutch. Many basic code readers only show the generic P0700; a scan tool that reads the transmission module shows the specific fault. Check fluid level and condition first, since low or burnt fluid causes many transmission codes.
P0720 symptoms
- Speedometer not working or erratic
- Erratic shifting or no upshifts
- ABS or traction warnings on some vehicles
Common causes of P0720
- Failed output speed sensor
- Damaged wiring or connector
- Damaged tone ring
How to diagnose P0720
- Check whether the speedometer works
- Inspect the sensor and wiring
- Compare output speed with wheel speeds on a scan tool
Can you drive with P0720?
With caution: shifting and the speedometer may be unreliable.
P0720 tips
On many trucks the output speed sensor also feeds the speedometer and cruise control, so a dead speedometer with erratic shifting is a strong clue. Check the connector for oil contamination and corrosion, which are common near the tail housing.
Will P0720 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0720 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0715 | Input/Turbine Speed Sensor A Circuit |
| P0700 | Transmission Control System Malfunction |
Guides that help
When it is more than a sensor
If the fault turns out to be internal (worn clutches, a failed converter or a damaged valve body), compare a rebuild with a replacement in transmission rebuild vs replacement and transmission replacement cost, identify your unit with what transmission do I have?, and browse our transmissions.
More guides: bad transmission speed sensor symptoms.
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