Failled emission po720

Hello, That is indicative of the output speed sensor for the transmission, but may be support systems for the sensor; explanation: The sensor is just an extension of the transmission control module or powertrain control module. Since it is an extension, it must have a circuit to supply power from the control module and signal back to the control module. Since P0720 says there is an issue with the output speed sensor, the interpretation is that the signal from the output speed sensor is not reaching the control module, or the control module is not sending that information to the instrument cluster or ABS control module. Test for reference voltage from the control module, test for signal voltage from the sensor, test for continuity for the return voltage, and check to see if your speedometer works.