P0721 means Output Speed Sensor Circuit Range/Performance. The output shaft speed signal is present but erratic or out of line with the other speed signals. 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 P0721 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.
P0721 symptoms
- Erratic or dead speedometer on many vehicles
- Harsh or erratic shifts
- Cruise control not working
Common causes of P0721
- Failing sensor
- Debris on the sensor tip
- Damaged wiring or connector near the tail housing
- Worn output shaft bearing or tone ring
How to diagnose P0721
- Watch output speed on a scan tool while driving
- Inspect and clean the sensor and connector
- Check wiring along the transmission
Can you drive with P0721?
Short distances; speedometer and shifts may be unreliable.
P0721 tips
Output speed sensors near the tail housing often suffer from oil-soaked or corroded connectors; clean and reseal the connector.
Will P0721 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 P0721 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 |
|---|---|
| P0720 | Output Speed Sensor Circuit |
| P0722 | Output Speed Sensor Circuit No Signal |
| P0500 | Vehicle Speed Sensor A 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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