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P0720 — Transmission Output Speed Sensor Malfunction

P0720 is set when the transmission control module does not receive a valid signal from the output shaft speed sensor. The TCM uses this signal to compare actual transmission output to expected output for the selected gear and engine RPM — if the signal is missing or implausible, gear ratio calculations fail and the TCM cannot shift correctly. The vehicle typically drops into limp mode (stuck in a default gear, often 3rd or 4th) until the signal is restored.

P0720 means transmission output speed sensor malfunction. A vehicle usually stays drivable short-term with this code, but it should be diagnosed promptly. The most common cause is failed output shaft speed sensor element (typically $150–$500). Causes and cost vary by make and model; confirm the root cause before replacing parts.

Severity: high powertrain Safe to drive (short term)

Reviewed by MECH AI Editorial · Last verified

What does P0720 mean?

P0720 is set when the transmission control module does not receive a valid signal from the output shaft speed sensor. The TCM uses this signal to compare actual transmission output to expected output for the selected gear and engine RPM — if the signal is missing or implausible, gear ratio calculations fail and the TCM cannot shift correctly. The vehicle typically drops into limp mode (stuck in a default gear, often 3rd or 4th) until the signal is restored.

What are the symptoms of P0720?

What causes P0720?

Cause Likelihood Estimated repair (USD)
Failed output shaft speed sensor element Most common $150–$500
Damaged sensor connector or harness Common $80–$350
Metal debris on the sensor tip (from internal transmission wear) — Cleaning the sensor face is a free first attempt. Common $100–$400
Damaged tone ring or reluctor wheel inside the transmission Occasional $1,500–$4,500
Transmission fluid contamination preventing the sensor from reading Occasional $200–$700
Wiring fault between the sensor and the TCM Occasional $100–$500
Failed TCM signal input (rare) Rare $500–$1,500

Repair costs are typical US ranges and vary by make, model, model year, and labor rate. A diagnostic trouble code is a symptom, not a guaranteed failed part — confirm the root cause before replacing anything.

Is it safe to drive with P0720?

In most cases a vehicle stays drivable for short trips with P0720 active, but you should diagnose and repair it promptly. This is a high-severity code — ignoring it can lead to further damage or a failed emissions test. Exact tolerance depends on your specific make and model.

How to diagnose P0720

  1. Locate the output speed sensor on this transmission

    The output shaft speed sensor is typically a two-wire sensor threaded into the rear of the transmission case (RWD vehicles) or the side of the transaxle (FWD vehicles). Some vehicles have it on the transfer case for 4WD. Confirm location in the service manual.

    Tools: Vehicle-specific service information

  2. Check connector and visible wiring

    Sensor connectors near the transmission case are exposed to heat, road debris, and sometimes fluid leaks. Unplug and inspect for corrosion, transmission fluid migration up the harness, or visible damage. Clean and re-seat.

    Tools: Connector unlock tool, Electrical contact cleaner

  3. Measure sensor resistance

    Most output speed sensors are magnetic or Hall-effect with a typical resistance of 200–1500 Ω. Compare to the service manual. Infinite resistance means an open sensor; near zero means shorted. Either way, replace.

    Tools: Multimeter, Service spec sheet

  4. Verify signal output during rotation

    On a lift with the rear wheels free to rotate, spin a rear wheel slowly by hand while watching the output speed PID. The reading should change in proportion to wheel rotation. No response confirms a dead sensor or damaged tone ring.

    Tools: Vehicle lift, Scan tool with output speed PID

  5. Inspect sensor tip for debris

    Remove the sensor and look at the magnetic tip. Steel slivers stuck to the magnet are normal — large chunks or clutch material is a warning sign that the transmission is shedding material. Clean the tip and reinstall as a first attempt; consider transmission fluid analysis if heavy debris was present.

    Tools: Socket, Magnet pick or wire brush

How do I fix P0720?

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P0720: frequently asked questions

What does diagnostic trouble code P0720 mean?

P0720 is set when the transmission control module does not receive a valid signal from the output shaft speed sensor. The TCM uses this signal to compare actual transmission output to expected output for the selected gear and engine RPM — if the signal is missing or implausible, gear ratio calculations fail and the TCM cannot shift correctly. The vehicle typically drops into limp mode (stuck in a default gear, often 3rd or 4th) until the signal is restored.

What are the symptoms of P0720?

Check Engine Light is illuminated. Speedometer reads zero or fluctuates erratically. Transmission locked into a single gear (limp mode). Hard, harsh, or no shifts. Cruise control inoperative. Vehicle may shudder or hesitate at the moment of shift. Often paired with P0700 (transmission control malfunction)

What causes P0720?

Failed output shaft speed sensor element (most-common). Damaged sensor connector or harness (common). Metal debris on the sensor tip (from internal transmission wear) (common). Damaged tone ring or reluctor wheel inside the transmission (occasional). Transmission fluid contamination preventing the sensor from reading (occasional). Wiring fault between the sensor and the TCM (occasional). Failed TCM signal input (rare) (rare)

Is it safe to drive with P0720?

In most cases a vehicle stays drivable for short trips with P0720 active, but it should be diagnosed and repaired promptly — this is a high-severity code. Ignoring it can lead to further damage or a failed emissions test. Specific tolerance varies by make and model.