P0720: Output Speed Sensor Circuit Malfunction
Updated November 14, 2026
The output speed sensor tells the transmission computer how fast the transmission's output shaft is turning. It uses this with the input speed to control shifts and check for slipping, and on many vehicles it also drives the speedometer. P0720 means the signal is missing or electrically faulty, and many transmissions go into a fail-safe mode with limited gears.
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🔧 Want to check this yourself? An OBD2 scanner reads the code; models with live data also show the sensor readings used in the checks below. See code readers and scanners from $24.99 ↓ · Which scanner do I need?
Common causes
- A failed output speed sensor
- Damaged wiring or a loose, corroded or fluid-soaked connector at the sensor
- Metal debris on a magnetic sensor tip
- A transmission control module fault (less common)
Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.
Symptoms
- Check engine or transmission warning light
- Speedometer that drops out, jumps or reads zero on many vehicles
- Harsh, delayed or erratic shifting
- Transmission stuck in one gear (limp mode)
- Cruise control not working
Is it safe to drive?
If the transmission is stuck in one gear, slipping, or shifting so harshly that the car won't accelerate properly, stop driving and have it towed. If it shifts normally with a steady light, drive gently and get it checked soon; if the speedometer is unreliable, keep with traffic and use a phone GPS app to judge your speed.
How to check it with a scanner
- Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
- Scan the transmission and ABS modules for other codes, especially input speed sensor, vehicle speed and gear ratio codes.
- Check the transmission fluid level and condition using your vehicle's procedure; some must be checked warm with the engine running, so keep hands clear of the belts and fan.
- With the engine off, inspect the sensor connector and wiring for damage, corrosion or fluid inside the connector.
- If you remove the sensor, check the tip for metal debris, which can also be a sign of internal wear.
- After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.
A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.
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Questions
What does P0720 mean?
P0720 is the generic OBD2 code for "Output Speed Sensor Circuit Malfunction." The output speed sensor tells the transmission computer how fast the transmission's output shaft is turning. It uses this with the input speed to control shifts and check for slipping, and on many vehicles it also drives the speedometer. P0720 means the signal is missing or electrically faulty, and many transmissions go into a fail-safe mode with limited gears.
Is it safe to drive with P0720?
If the transmission is stuck in one gear, slipping, or shifting so harshly that the car won't accelerate properly, stop driving and have it towed. If it shifts normally with a steady light, drive gently and get it checked soon; if the speedometer is unreliable, keep with traffic and use a phone GPS app to judge your speed.
How do I check P0720 myself?
Read the code and freeze-frame data with an OBD2 scanner, then: Scan the transmission and ABS modules for other codes, especially input speed sensor, vehicle speed and gear ratio codes. Check the transmission fluid level and condition using your vehicle's procedure; some must be checked warm with the engine running, so keep hands clear of the belts and fan. With the engine off, inspect the sensor connector and wiring for damage, corrosion or fluid inside the connector. If you remove the sensor, check the tip for metal debris, which can also be a sign of internal wear.
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