The output speed signal from the gearbox is erratic. Gear selection and torque converter lock-up depend on it, so shifts become unpredictable.
P0721 — also written PO721, P 0721, 0721 — is the OBD-II code for output speed sensor circuit range/performance. Same code, same fix: this page covers every spelling of it.
P0721 is a transmission fault code, typically costing £150–£650 to put right in a UK garage.
What causes P0721?
- Failed output speed sensor
- Damaged reluctor teeth
- Chafed wiring under the car
- Low fluid
How P0721 is fixed
- Compare output speed with wheel speed on live data
- Replace the sensor
- Repair the loom
P0721 repair cost in the UK
Most P0721 repairs land between £150–£650 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Can you drive with P0721?
Drive gently to a garage.
Urgency: high.