P0720 — Output Speed Sensor Circuit

OBD-II trouble code P0720 indicates an issue with the output speed sensor circuit, a critical component used by the vehicle’s Engine Control Unit (ECU) to monitor the output shaft speed. When this code appears, it suggests the ECU has detected a problem in the electrical circuit that transmits the speed signal from the sensor to the ECU. It’s important to note that labels and diagnostic trouble code (DTC) designations may vary between vehicle manufacturers, but the underlying fault remains similar.

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Manufacturer variations for trouble code P0720

Different vehicle manufacturers may label the P0720 code differently in their diagnostic systems or on their trouble code lists. While the core fault remains the same—related to the output speed sensor circuit—OEMs sometimes assign distinct labels for clarity or internal classification purposes.

Known label variations include:

• Ford: « Output Shaft Speed Sensor Circuit Malfunction »
• Honda: « Output Speed Sensor Signal Malfunction »
• Volkswagen: « Transmission Output Speed Sensor Circuit »
• BMW: « Drive Shaft Speed Sensor Erroneous Signal »
• Hyundai/Kia: « Output Speed Sensor Circuit Fault »

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What does trouble code P0720 mean?

In simple terms, P0720 signals that the ECU is detecting an abnormality in the circuit that transmits the output shaft speed data from the sensor to the vehicle’s computer system. This sensor, typically mounted on the transmission or gearbox, provides vital information used to control gear shifting, torque converter lock-up, and overall transmission operation.

The ECU monitors the sensor’s electrical signals, and if the voltage or frequency readings are outside expected parameters, it interprets this as a fault, setting the code. This can happen due to a faulty sensor, damaged wiring, or connector issues.

This code often appears in contexts of shifting problems, transmission warning lights, or after sensor-related repairs. It may also be detected during routine emissions tests or diagnostics.

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Severity and risks of trouble code P0720

P0720 is classified as a moderate issue, as it can impact the transmission’s performance and potentially cause shifts to become rough or unpredictable. If left unattended, it might lead to more serious damage to the transmission control system or other related components.

While the vehicle may still be able to operate, driving with this fault could result in safety concerns or further mechanical damage. The vehicle could shift improperly, exhibit poor performance, or trigger warning lights.

**Can the vehicle be driven?** Limited — it’s generally safe to drive temporarily but should be diagnosed and repaired promptly to avoid further damage.

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Symptoms of trouble code P0720

Drivers may notice subtle or overt signs indicating an issue with the output speed sensor circuit. Common symptoms include:

• Transmission shifting irregularly: Jerky, delayed, or harsh shifts
• Transmission warning light: Illuminates on the dash
• Loss of power or surging: Especially during acceleration
• Vehicle stuck in limp mode: Limited power and speed recovery
• Unusual noises or vibrations: During gear changes
• Inconsistent or erratic tachometer readings: Display fluctuations

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Most likely causes of trouble code P0720

Diagnosing P0720 often involves considering various potential causes. Generally, these causes are ranked from most to least common based on typical failure modes:

1. Faulty output shaft speed sensor: The sensor itself may be defective due to age, wear, or electrical failure.
2. Damaged wiring or connector issues: Corrosion, broken wires, or loose connections impair signal transmission.
3. Transmission control module (TCM) or ECU malfunction: Rare, but possible if the modules’ internal circuitry is compromised.
4. Internal transmission issues: Such as gear wear or mechanical faults affecting sensor operation.

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How to diagnose trouble code P0720

Diagnosis should always be systematic, beginning with basic visual and electrical checks before moving to live data analysis and testing. Here are standard steps:

1. Visually inspect the wiring harness and connector at the output speed sensor for damage, corrosion, or disconnection.
2. Check the wiring continuity using a multimeter to ensure no open or short circuits exist.
3. Test the sensor’s resistance (if applicable) to verify it falls within manufacturer specifications.
4. Use a scan tool to view live data: Observe the sensor output signal during vehicle movement. Look for inconsistent or no signal.
5. Verify proper voltage supply and ground connections to the sensor.
6. Consider swapping with a known-good sensor if accessible, to confirm sensor failure.

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Possible repairs for trouble code P0720

Addressing P0720 often involves replacing faulty components or fixing wiring issues. Depending on the root cause, repairs can range from simple to complex. Typical solutions include:

• Replacing the output shaft speed sensor: Usually a straightforward repair, suitable for DIY if the part is accessible.
• Repairing or replacing wiring and connectors: Ensures proper electrical contact and signal transmission. This is a professional job, especially if wiring repair requires specialized tools.
• Cleaning or securing connections: Simple but effective, especially if corrosion is present.
• Reprogramming or replacing the transmission control module (TCM): Usually requires professional diagnostic tools and software.
• Internal transmission repairs: Such as replacing worn gear components, which is typically handled by transmission specialists.

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Vehicles commonly associated with trouble code P0720 in Europe

While P0720 can occur in various makes and models, certain vehicle types are more frequently affected, especially those with automatic transmissions relying heavily on output speed sensors. Here are some examples grouped by brand:

• Ford: Focus, Fiesta, Transit
• VW / Audi / Skoda / Seat: Golf, Passat, A3, Leon
• BMW: Series 3, 5, 7
• Hyundai/Kia: Elantra, Cerato, Sportage
• Peugeot / Citroën: 208, 308, C4, C5

Specific model years and engine types vary, and this list is not exhaustive. Diagnostic history and OEM data should always be consulted for precise vehicle targeting.

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Frequent mistakes with trouble code P0720

Diagnosing and repairing P0720 can sometimes lead to errors if not approached carefully. Common mistakes include:

• Replacing parts without proper testing: Swapping the sensor or wiring without confirming the root cause.
• Ignoring electrical issues: Focusing only on the sensor when wiring or connector problems may be the actual source.
• Overlooking live data interpretation: Relying solely on code readout without real-time sensor signals can mislead diagnosis.
• Neglecting to clear codes after repair: Failing to turn off the MIL (Malfunction Indicator Lamp) to verify repair efficacy.
• Failing to consider related codes: Other transmission or sensor-related codes may be relevant and should be diagnosed in tandem.

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Quick FAQ — trouble code P0720

Can this code disappear on its own? Typically, no. Once set, the code remains until the underlying issue is resolved and the ECU detects that the fault no longer exists. Some temporary electrical anomalies might clear if the issue was transient, but persistent problems require diagnosis and repair.

Can I keep driving? Limited. While it’s possible to drive the vehicle temporarily, it’s recommended to get the issue diagnosed as soon as possible to prevent further transmission damage or operational problems.

Why does the code return after clearing? Because the underlying cause—say, a faulty sensor, wiring problem, or connector—is still present, the ECU re-detects the fault once the system performs its self-checks again.