P1721 – Gear 1 Incorrect Ratio

P1721 Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P1721 Possible Causes

Faulty Vehicle Speed Sensor,Vehicle Speed Sensor harness is open or shorted,Vehicle Speed Sensor circuit poor electrical connection,Transmission Control Module (TCM) communication

P1721 Description

The vehicle speed sensor??TR signal is transmitted from combination meter to Transmission Control Module (TCM) by CAN communication line. The signal functions as an auxiliary device to the revolution sensor when it is malfunctioning. The TCM will then use the vehicle speed sensor??TR signal.