P0720
Output Speed Sensor Circuit
If your vehicle's onboard computer has flagged the diagnostic trouble code P0720, it refers to a detected anomaly regarding "Output Speed Sensor Circuit". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
Your vehicle's computer logged P0720 after detecting a malfunction in the output speed sensor circuit system. In practice, this fault causes speedometer stops working, erratic shifting, vehicle stuck in limp mode. Given the high severity of this code, continuing to drive risks significant mechanical damage. Have it diagnosed immediately.
Symptoms
Speedometer stops working, erratic shifting, vehicle stuck in limp mode
Common Causes
- Defective output speed sensor (OSS)
- Metal shavings on the magnetic sensor
- Wiring open or shorted
- Internal transmission failure
How to Fix
- 1 Remove and clean or replace OSS
- 2 Inspect wiring harness for damage
- 3 Check transmission fluid for heavy metal debris
- 4 Replace transmission speed sensor
Technical Explanation
The ECM detects code P0720 by continuously monitoring the relevant sensor circuit against calibrated threshold values stored in its non-volatile memory. The TCM compares the ratio between input turbine speed sensor and output speed sensor readings against the expected gear ratio stored for each commanded gear position. A deviation greater than a few percent indicates clutch slippage, solenoid malfunction, or internal mechanical failure. The MIL illuminates after the fault is confirmed on two consecutive drive cycles, and the freeze frame data captured at first detection is stored in the PCM's memory for diagnostic reference.
Is It Safe to Drive?
An active P0720 code under high-severity conditions means the affected system is operating outside safe parameters. Continued driving — especially under load or at highway speeds — significantly increases the risk of secondary damage to components like metal shavings on the magnetic sensor.
Mechanic's Pro Tip
Before replacing any component on P0720, spend 5 minutes inspecting the wiring harness and connector first — corrosion, chafed insulation, and backed-out pins cause the majority of these faults and cost nothing to fix. Use a multimeter to measure voltage drop across the connector pins under load; anything above 0.1V indicates excessive resistance that will cause intermittent failures even after replacing the sensor.
OSS Sensor replacement: $150 - $350