DTC P0721 Output Speed Sensor Circuit Performance
DTC P0721 - Output Speed Sensor Circuit Performance
Conditions for Running the DTC
• The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 9V and less than 32V (24V TCM).
• Output speed is above 200 rpm.
• Shift is complete and range attained is not neutral.
• For fire truck vocation, pump not pumping.
Conditions for Setting the DTC
DTC P0721 sets when one of the following two conditions occur:
• Unrealistic large changes in output speed. Failure is set if an unrealistic change in transmission output speed is detected at or above 500 rpm for 0.15 seconds.
• Noisy output speed. Noise is determined with two counters. A low counter is incremented when output speed change is below 500 rpm for 80 samples. A high counter is incremented when output speed change is above 800 rpm. When both counters accumulate 5 events, a failure is set.
Actions Taken When the DTC Sets
When DTC P0721 is active, the following conditions occur:
• If failure occurs while in a forward range and a shift has been completed, the transmission will remain in the current range.
• If failure occurs while in a forward range and a shift is in progress, the transmission will return to the previous range, except in post-shift state, then the transmission will continue to the commanded range.
• DTC P0721 is stored in TCM history.
• The CHECK TRANS light illuminates.
• The TCM inhibits TCC engagement.
• The TCM freezes shift adapts.
Conditions for Clearing the DTC/CHECK TRANS Light
Use the Allison DOC™ For PC–Service Tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.
Diagnostic Aids
• Inspect the wiring for poor electrical connections at the TCM and service brake switch. Look for the following
conditions:
→A bent terminal
→A backed-out terminal
→A damaged terminal
→Poor terminal tension
→A chafed wire
→A broken wire inside the insulation
• You may have to drive the vehicle in order to experience a fault.
• If the condition is intermittent, connect the Allison DOC™ For PC–Service Tool and observe the speed sensor indicated by the code. If the signal is erratic, investigate and eliminate the following:
→Intermittent wiring connection
→Excessive vibration (driveline or engine torsionals)
→Irregular sensor gap (loose sensor, loose tone wheel, or damaged tone wheel)
• Install a known good speed sensor and see if normal function is restored to rule out an internal short or open in the sensor removed.
• Check that the speed sensor wiring consists of twisted pairs at the rate of 12 to 16 twists per 300 mm. These twists must extend the entire length of the wiring harness to within at least 50 mm of the speed sensor connector.
• Install a known good TCM, if available. If the DTC does not return, reinstall the old TCM to verify the repair.
#Test Description
The numbers below refer to step numbers on the diagnostic table.
4. Tests for proper ignition voltage.
→Install the Allison DOC™ For PC–Service Tool.
→Start the Engine.
→Record the failure records.
→Clear the DTCs.
→Using Allison DOC™ For PC–Service Tool, measure ignition voltage. Is voltage within specified values? (9–18V for 12V TCM, and 18–32V for 24V TCM).
5. Tests for proper output speed sensor resistance at the OEM-side of the harness.
→Turn ignition OFF.
→Disconnect the 80-way connector at the TCM.
→Using a DVOM, measure resistance between terminal 40 and terminal 60 at the OEM-side of the 80 way connector. Is the speed sensor resistance within the specified value?
6. Tests for output speed sensor resistance.
→Disconnect the wiring harness from the output speed sensor.
→Using a DVOM, check the resistance between the speed sensor terminals. Is the speed resistance within the specified value?
→Replace the output speed sensor (refer to appropriate service manual). Is replacement complete?
To verify the repair:
→Clear the DTC.
→Drive the vehicle under normal operating conditions.
→Use Allison DOC™ For PC–Service Tool to monitor output speed sensor operation.
Did the DTC return?
Read More:
Blog.Teknisi
0 Response to "DTC P0721 Output Speed Sensor Circuit Performance"
Post a Comment