Staff Answer
Jun 22, 2026 - 01:24 PM
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The P0720 error code stands for "Output Speed Sensor (OSS) Circuit." This indicates that the Transmission Control Module (TCM) or Engine Control Module (ECM) is not receiving a signal—or is receiving an erratic signal—from the sensor that monitors how fast the transmission output shaft is rotating.
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Inspect Sensor Wiring: Locate the Output Speed Sensor on the transmission housing. Inspect the wiring harness for signs of physical damage, chafing, or exposed copper. Check the connector for pins that are bent, pushed back, or corroded.
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Check for Signal Interference: The OSS is a magnetic sensor. Ensure there is no significant debris or metallic shavings stuck to the sensor tip. Clean the area around the sensor before removing it.
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Test Sensor Resistance: Use a multimeter to check the internal resistance of the sensor. Compare this to the manufacturer's specifications. If the sensor shows an open circuit or no resistance, the internal coil is likely burnt out.
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Check for Internal Transmission Issues: In some cases, the gear that the sensor monitors inside the transmission may be damaged or loose, causing a weak or missing signal.
Note: Because this signal is critical for shift timing and speedometer accuracy, you may notice harsh or delayed shifting, speedometer failure, or the vehicle entering "limp mode." Clear the code with an OBDII scanner after performing repairs to reset the transmission shift logic.
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