DTC Advanced Diagnostics: P0721
DTC P0721:Output Shaft (Countershaft) Speed Sensor (Range/Performance)

General Description


The output shaft (countershaft) speed sensor is attached to the outside of the transmission housing. The output shaft (countershaft) speed sensor generates a pulsing signal according to the speed of the park gear on the output shaft (countershaft). Using that signal, the powertrain control module (PCM) determines the speed of the output shaft (countershaft). If no pulses occur with the output shaft (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 output shaft (countershaft) speed sensor and the input shaft (mainshaft) speed sensor, the PCM detects a malfunction and stores a DTC.

Monitor Execution, Sequence, Duration, DTC Type, OBD Status
Execution
Continuous
Sequence
None
Duration
10 seconds or more
DTC Type
One drive cycle, MIL on, A/T gear position indicator blinks
OBD Status
PASSED/FAILED/NOT COMPLETED (STILL TESTING)

Enable Conditions
Condition
Minimum
Maximum
Engine speed
[ENGINE SPEED]
500 rpm
–
Vehicle speed
[VEHICLE SPEED]
13 mph (20 km/h)
–
Battery voltage
[BATTERY VOLTAGE]
11 V
–
Shift lever position
D, S
No active DTCs set (prevents monitor from running)
P0705, P0706, P0716, P0717, P0722, P0962, P0963, P0966, P0967, P0970, P0971, P0973, P0974, P0976, P0977, P0979, P0980, P2720, P2721
Other
Not during shifting
Not when the shift lever is being shifted
No electrical noise in the input shaft (mainshaft) speed sensor output circuit
Except 1st gear
[ ]: HDS Parameter

Malfunction Threshold
The vehicle speed measured by the input shaft (mainshaft) speed sensor [Input Shaft (Mainshaft) Speed (rpm)] divided by the vehicle speed measured by the output shaft (countershaft) speed sensor [Output Shaft (CounterShaft) Speed (rpm)] is greater than 7.0 for at least 10 seconds.

Possible Cause
NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
Output shaft (countershaft) speed sensor line short to ground
Output shaft (countershaft) speed sensor line open (includes connector loose connection or disconnection)
Output shaft (countershaft) speed sensor failure
PCM internal circuit failure

Confirmation Procedure
Operating Condition
1.
Start the engine.
2.
Drive the vehicle at a speed of 13 mph (20 km/h) or more for at least 10 seconds.
Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
With the HDS
None.

Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected, the MIL comes on, the A/T gear position indicator blinks, and a Pending DTC, a Confirmed DTC, and the freeze data are stored in the PCM memory.

Conditions for clearing the DTC
The A/T gear position indicator comes off by pressing the engine start/stop button to select the OFF mode. The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command.