What does it mean?
OBD II code P0722 is a generic code that is defined as “Output shaft speed (OSS) sensor -no signal”, and is set when the PCM (Powertrain Control Module) fails to detect a signal from the transmission output shaft speed sensor. Most, if not all output shaft speed sensors consist of a reluctor wheel or ring whose teeth interrupt a magnetic field, thereby creating a series of pulse that the PCM interprets as a rotational speed.
While the output shaft speed sensor is the primary driver of the speedometer to indicate vehicle speed, it also provides input data to the PCM, which data is used to calculate appropriate transmission shift strategies. In a fully functional system, the PCM expects to see a steady increase in the rotational speed of the transmission as the vehicle accelerates.
This information is compared to input data from the engine speed sensor, throttle position sensor and other engine driveability sensors, and when a pre-determined shift point is reached (based on information obtained from all relevant sensors), the PCM will instruct the TCM (Transmission Control Module) to initiate an appropriate gear shift.
Thus, if the PCM does not receive an input signal from the transmission output shaft speed sensor, it is effectively deprived of the primary information it needs to control the transmission. When this happens the PCM will set code P0722, and may also illuminate a warning light. Note that on some applications, several failure cycles must occur before a warning light is illuminated. The image below shows a typical transmission output shaft speed sensor.
Note though that the design, appearance of output shaft speed sensors vary greatly between applications; nonetheless, this sensor is almost always located close to the transmission output shaft.