What it means
The transmission output speed sensor signal is missing or implausible. The TCM uses this signal together with input speed to determine actual gear ratio; many vehicles also use it as a backup vehicle speed signal for the cluster and ECU.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The transmission output speed sensor measures how fast the transmission's output shaft is turning, and the control module uses that reading to manage shifts and compare actual speed with expected gear operation. P0720 sets when the module detects a malfunction in the sensor circuit, such as a missing or implausible signal.
Common causes
Most likely first.
- Output speed sensor failed
- Wiring or connector fault
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Read freeze-frame data and live output-speed data to determine whether the signal is absent or implausible and under what driving conditions the fault set.
- Compare output speed with vehicle speed and transmission input speed in live data while driving only if the vehicle shifts safely.
- Inspect the output speed sensor connector and nearby harness for looseness, corrosion, fluid intrusion, or damage.
- Check the sensor mounting and wiring routing for looseness, chafing, or damage near the transmission.
- Use the wiring diagram to test the output speed sensor circuit and sensor signal against the manufacturer's specification before replacing parts.
Common fixes
- Reconnect or clean a loose or corroded output speed sensor connector.
- Repair damaged or chafed output speed sensor wiring.
- Secure a loose sensor mounting if applicable.
- Replace the output speed sensor if its circuit and signal tests identify it as faulty.
Can I keep driving?
Because incorrect output-speed data can cause erratic shifts or limp mode, avoid high-speed driving and heavy loads. Stop if the transmission slips or loses predictable shifting.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.