P0720: Output Speed Sensor — Causes and Fix
Table of contents
Key Takeaway
P0720 is the output speed sensor. It monitors how fast the transmission output shaft spins.
P0720 means the output speed sensor
What P0720 Means
The output speed sensor measures the transmission output shaft speed. The TCM uses this to determine vehicle speed and compare it against input speed for shift control. See our [OBD-II codes pillar](/codes/) for related transmission codes.
Symptoms
| Symptom | Why |
|---|---|
| Speedometer reads zero or erratic | Output sensor feeds speedometer |
| Harsh shifting | TCM cannot verify shift completion |
| No shifting (one gear only) | TCM enters limp mode |
| ABS/traction lights on | Systems use vehicle speed data |
| Cruise control inoperative | No reliable speed input |
Common Causes
| Cause | Fix Cost |
|---|---|
| Failed sensor | $80 – $200 |
| Wiring/connector issue | $50 – $200 |
| Metal debris on sensor | $0 (clean) |
| Old transmission fluid | $100 – $200 |
STEER reads transmission speed data live
Confirming a P0720 typically requires comparing the output sensor reading against the input sensor reading or against the actual vehicle speed. The [STEER OBD-II adapter](/obd2-scanner/) reads both transmission speeds live, so the difference between a failed sensor and a real transmission slip becomes obvious in 60 seconds without a shop diagnostic.
Frequently Asked Questions
What does a P0720 code mean on my car?
The output speed sensor on the transmission has failed or its signal is invalid. The TCM uses this sensor to know how fast the output shaft is spinning, which it uses for vehicle speed calculations and for verifying that shifts completed properly. When the sensor fails, the TCM cannot trust its shift logic, and symptoms range from speedometer issues to harsh shifting to limp mode.
Can I drive my car with a P0720 code?
For short distances at moderate speed, usually yes. The car remains drivable but symptoms include erratic speedometer (you cannot trust the indicated speed), harsh shifts, and potentially limp mode. Avoid highway driving and high-load conditions until repaired. If the speedometer reads zero entirely, drive with extra caution because cruise control and several safety systems may be inoperative.
How do I replace a transmission output speed sensor?
On most rear-wheel-drive trucks and SUVs the sensor threads into the transmission tail housing or extension housing — typically 10-20 minutes to replace with a single wrench, no fluid drain needed. On front-wheel-drive cars the sensor is often more difficult to access, possibly requiring removal of a wheel, splash shield, or other components. Cost: $50-$150 for the sensor, $0-$200 in labor.
Will a P0720 turn off my speedometer?
Often yes. Most modern vehicles feed the output speed sensor signal directly to the instrument cluster for the speedometer reading. When the sensor fails, the speedometer reads zero or fluctuates erratically. Some vehicles use a separate vehicle speed sensor or wheel speed sensor for the speedometer, in which case the speedometer may continue working while the transmission code remains active.
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