P0720
Output Speed Sensor Circuit MalfunctionP0720 is a generic OBD-II powertrain diagnostic trouble code: Output Speed Sensor Circuit Malfunction. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0720 means
P0720 is stored when the TCM detects a malfunction in the Output Speed Sensor (OSS) circuit — also referred to as the transmission output shaft speed sensor or Vehicle Speed Sensor (VSS) depending on the platform. This sensor generates a frequency-based signal proportional to the rotational speed of the transmission output shaft, which the TCM uses to calculate actual vehicle speed, determine gear ratios, manage torque converter lock-up, and coordinate shift points.
The code sets when the TCM receives no signal, an implausibly low signal, or a signal that is erratic relative to other speed inputs such as the Input Shaft Speed (ISS) sensor or the ABS wheel-speed sensors. Common root causes include a failed sensor (magnetic pickup or Hall-effect type), damaged tone-wheel teeth on the output shaft, damaged or corroded wiring in the sensor circuit, or contamination from metallic debris in the transmission fluid adhering to the sensor tip.
Because vehicle speed data is shared with the ABS, traction control, cruise control, and instrument cluster, a faulty OSS can trigger multiple additional DTCs across several modules.
Common causes
Most-frequently reported root causes when P0720 is logged.
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1
Failed Output Speed Sensor (OSS) — open coil, cracked body, or failed Hall-effect element
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2
Metallic debris from internal transmission wear adhering to the sensor's magnetic tip
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3
Damaged, corroded, or chafed wiring and connector in the OSS circuit
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4
Damaged or missing teeth on the output shaft tone ring/reluctor wheel
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5
Incorrect sensor air gap (sensor not seated fully or shim missing)
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6
Low or severely degraded transmission fluid allowing debris accumulation near the sensor
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7
Faulty TCM or shared vehicle speed circuit fault affecting multiple modules (rare)
Symptoms drivers notice
How to diagnose P0720
A typical diagnostic flow when this code is present.
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1
Retrieve all DTCs from TCM and ABS modules; a concurrent C0035/C0040 wheel-speed fault or U-code may indicate a broader shared-signal problem
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2
Check transmission fluid level and condition — drain and inspect the pan for metallic debris, which may indicate internal damage requiring further teardown
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3
Inspect the OSS connector and wiring harness for corrosion, damage, or chafing against the exhaust or chassis; repair as needed
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4
With a DVOM, verify sensor supply voltage or resistance against OEM specification; for Hall-effect sensors, verify 5 V or 12 V supply and a clean square-wave output while rotating the output shaft by hand or during a slow roll
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5
Inspect the tone ring for chipped or missing teeth using a mirror and flashlight through the sensor port; replace the ring or output shaft assembly if damaged
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6
Replace the OSS if the circuit wiring is sound but sensor output is absent or irregular, ensuring correct seating and air gap
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7
Clear codes, road-test at varied speeds, and confirm no re-set using live-data comparison between OSS and wheel-speed readings
Related powertrain codes
- P0700 — Transmission Control System Malfunction
- P0701 — Transmission Control System Range/Performance
- P0702 — Transmission Control System Electrical
- P0703 — Torque Converter/Brake Switch B Circuit Malfunction
- P0704 — Clutch Switch Input Circuit Malfunction
- P0705 — Transmission Range Sensor A Circuit malfunction (PRNDL Input)
Frequently asked questions
Why did P0720 also turn on my ABS warning light?
Vehicle speed data from the OSS is often shared with the ABS module. When the OSS signal is absent or erratic, the ABS module may lose its reference speed, triggering its own fault codes and disabling traction control and stability control alongside the transmission fault.
Is it safe to drive with P0720?
Only for a short distance at low speed if absolutely necessary. ABS and traction control may be disabled, and the transmission may be locked in limp mode. Highway driving is not recommended.
How do I know if it's the sensor or the tone ring?
With the sensor removed, physically inspect the tone ring teeth through the sensor bore — any chipped, cracked, or missing teeth confirm ring damage. If the ring is intact, test the sensor resistance or waveform output; no output on an intact ring points to a dead sensor.
Can I clean the OSS rather than replace it?
If the sensor tip is coated in metallic debris but the coil or Hall element is undamaged, cleaning and re-installing may temporarily restore function. However, heavy debris accumulation usually indicates internal transmission wear; inspect the pan and fluid thoroughly before simply cleaning and re-fitting the sensor.
Disabling P0720 in software
RaceTune can permanently disable P0720 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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