Possible causes

– Faulty Speed Sensor
– Speed Sensor harness is open or shorted
– Speed Sensor circuit poor electrical connection

When is the code detected?

Vehicle speed sensor above 1 MPH and the ECM detected noise interference from the output speed sensor

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Speedometer improper reading
– Possible shifting problems

P0721 FORD Description

The speed sensor detects the revolution of the idler gear parking pawl lock gear and emits a pulse signal. The pulse signal is sent to the Transmission Control Module (TCM) which converts it into vehicle speed.

FORD Technical Service Bulletins for P0721 code