DTC P0721
DTC P0721 : Countershaft Speed Sensor Performance
General Description
The countershaft speed sensor is attached to the outside of the transmission housing. The countershaft speed sensor generates different frequency pulse signal depending on the rotating speed of the countershaft driven gear. The pulse signal is transmitted to the transmission control module (TCM) and used for measurement of the countershaft speed. When there is a missing pulse while the countershaft is rotating which occurs by open circuit, intermittent open circuit, and short circuit, the TCM detects as a malfunction. The countershaft speed sensor speed and the mainshaft speed sensor speed are compared, and if there is an abnormality in detected sensor speed ratio for a specified time, the TCM detects a malfunction and stores a DTC.
Monitor Execution, Sequence, Duration, DTC Type
| Execution | Continuous |
| Sequence | None |
| Duration | 2 seconds or more |
| DTC Type | One drive cycle, MIL on, shift position indicator blinks |
Enable Conditions
| Condition | Minimum | Maximum | |
|---|---|---|---|
| Vehicle speed [Vehicle Speed] | 13 mph (21 km/h) | - | |
| Other | Not while shifting | ||
| Not when the shift position/mode is being shifted | |||
| [ ]:HDS Parameter | |||
Malfunction Threshold
The rotation speed measured by the countershaft speed sensor is less than the rotation speed measured by the mainshaft speed sensor by a factor of 0.156 for at least 2 seconds.
Possible Cause
The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
- Countershaft speed sensor failure
- Countershaft speed sensor NC line open (includes connector loose connection or disconnection)
- Countershaft speed sensor VCC3 line open (includes connector loose connection or disconnection)
- Countershaft speed sensor SG3 line open (includes connector loose connection or disconnection)
- Countershaft speed sensor NC line short to ground
- TCM internal circuit failure
Confirmation Procedure
Operating Condition
- Start the engine.
- Test-drive the vehicle at speeds over 13 mph (21 km/h) for at least 2 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 shift position indicator blinks, and a Pending DTC, a Confirmed DTC, and the freeze data are stored in the TCM memory.
Conditions for clearing the DTC
The shift position indicator comes off by turning the vehicle to the OFF (LOCK) 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.