P0721 Code: Output Shaft Speed Sensor Circuit Range/Performance
🟠 Moderate severity · drivable
You can drive, but the speedometer may read wrong and the transmission may shift harshly or go into fail-safe mode.
What P0721 means
The output shaft speed sensor measures how fast the transmission's output shaft spins. The reading is out of the expected range. The computer compares this reading with engine speed and input shaft speed to check gear ratios and control shifting.
Symptoms
- Check engine light is on
- Speedometer reads wrong or doesn't work
- Harsh or delayed shifts
- Transmission slips or goes into fail-safe mode
Common causes
- most common: Faulty output shaft speed sensor
- common: Contaminated transmission fluid with metal debris
- common: Damaged wiring or loose connector
- less common: Worn internal transmission parts
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Check transmission fluid level and condition | Yes | $10–40 |
| Replace the output shaft speed sensor | Mechanic | $150–400 |
| Repair damaged wiring or connector | Mechanic | $80–250 |
Frequently asked questions
Can I drive with a P0721 code?
Yes, but the speedometer may read wrong and the transmission may shift harshly or go into fail-safe mode. Have it diagnosed soon.
What does the output shaft speed sensor do?
It measures how fast the transmission output shaft spins. The computer uses it with other speed readings to check gear ratios and control shifting.
How much does it cost to fix a P0721?
Replacing the sensor usually runs $150–$400 including parts and labor. If the fluid is full of debris, the transmission itself may need attention.
Related codes
P0723
P0723 Code: Output Shaft Speed Sensor Circuit Intermittent
P0720P0720 Code: Output Speed Sensor Circuit Malfunction
P0700P0700 Code: Transmission Control System Malfunction
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.