DTC P0726 Engine Speed Sensor Circuit Performance
P0726 - Engine Speed Sensor Circuit Performance
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Conditions for Running the DTC
• The test is enabled by calibration.
• Engine speed is above 600 rpm.
• Shift is complete and range attained is not neutral.
Conditions for Setting the DTC
DTC P0726 sets when one of the following conditions occur:
• Unrealistic large changes in engine speed. Failure is set if an unrealistic change in transmission Engine speed is detected at or above 600 rpm for 0.15 seconds.
• Noisy engine speed. Noise is determined with two counters. A low counter is incremented when Engine speed change is below 650 rpm for 80 samples. A high counter is incremented when Engine speed change is above 1050 rpm. When both counters accumulate 5 events, a failure is set.
Actions Taken When the DTC Sets
When DTC P0726 is active, the following conditions occur:
• DTC P0726 is stored in TCM history.
• The TCM does not illuminate the CHECK TRANS light.
• The TCM defaults Engine speed to turbine speed. Turbine speed is used to determine the missing Engine speed.
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 Engine speed sensor. 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, damaged torque converter ribs).
• 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.
2. 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).
3. Tests for proper engine 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 39 and terminal 59 at the OEM-side of the 80 way connector. Is the speed sensor resistance within the specified value?
4. Tests for Engine speed sensor resistance.
→Disconnect the wiring harness from the output speed sensor.
→Using a DVOM, measure the resistance between the speed sensor terminals. Is the speed sensor resistance within the specified value?
→Replace the engine speed sensor (refer to service manual). Is replacement complete?
To verify the repair:
→Clear the DTC.
→Drive the vehicle under normal operating conditions.
→Using Allison DOC™ For PC–Service Tool monitor engine speed sensor operation.
Did the DTC return?
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