P0720 Fault Code in Hyundai: Causes, Symptoms, and Fixes

P0720 indicates a fault in the output speed sensor (OSS) or its circuit. The Transmission Control Module (TCM) uses the OSS to determine vehicle speed and shifting points. When it fails or sends an incorrect signal, shifting issues and drivability problems can occur.

Common Symptoms:

1. Check Engine Light (CEL)
2. Speedometer not working or erratic
3. Harsh or delayed shifting
4. Transmission stuck in limp mode
5. Torque converter may not lock up
6. Possible ABS or traction control warning lights (in some vehicles)

Common Causes:

1. Faulty output speed sensor
2. Broken, shorted, or corroded wiring
3. Damaged or disconnected sensor connector
4. Faulty TCM
5. Internal transmission damage (rare)

Diagnostic Tips:

1. Use a scan tool to read transmission data (check if OSS shows any signal)
2. Inspect the wiring and connector for corrosion, damage, or loose pins
3. Test the sensor resistance with a multimeter (typically 250–1,500 ohms depending on vehicle)
4. Check for continuity in wiring from sensor to TCM
5. Compare input speed sensor vs output speed sensor readings

Possible Fixes:

1. Replace the output speed sensor
2. Clean or replace corroded or damaged wiring/connectors
3. Check and replace blown fuses or bad grounds
4. Reprogram or replace the TCM if needed