P0720: OBD-II code P0720 flags a fault in the output speed sensor circuit — the TCM can't determine transmission output shaft speed for shift scheduling.

Symptoms

• Check engine light is on; transmission may hold gears, shift erratically, or enter limp mode.
• Speedometer may be affected on vehicles that source vehicle speed from the output speed sensor.
• Cruise control may drop out because the speed reference is unreliable.

Common causes

• A failed output speed sensor with an open or shorted internal element.
• Damaged wiring or a corroded connector at the sensor on the transmission tail housing.
• A damaged reluctor wheel on the output shaft producing bad pulses that confuse the TCM.

What to do?

Read live output speed data during driving. Test sensor resistance. Replace the sensor if faulty. Inspect the reluctor wheel visually if a replacement doesn't clear the code.