DTC P0721: Problem in Output Shaft (Countershaft) Speed Sensor Circuit: General Description

The countershaft speed sensor is attached to the outside of the transmission housing. The countershaft speed sensor generates a pulsing signal according to the speed of the park gear on the countershaft. Using that signal, the powertrain control module (PCM) determines the speed of the countershaft. If pulse dropouts occur with the countershaft rotating, the PCM detects a malfunction that may be caused by an open, a temporary open, or a short to ground. Based on the velocity ratio measured by the mainshaft speed sensor and the countershaft speed sensor, a malfunction is detected and a DTC is stored.