P0763

ALLISON AUTOMATIC TRANSMISSION

DTC P0763





Test 1-6





Test 7-12

Circuit Description for Allison Automatic Transmission
Shift Solenoid C is a normally closed solenoid that provides the necessary logic to distribute fluid to the correct clutches. The shift solenoid provides either full pressure or exhaust to the head of Shift Valve C. Since the valve state (stroked or unstroked) is critical to providing the correct transmission range, the shift valve has a pressure switch (located in the pressure switch manifold) which provides feedback to the computer as to the valve's position.
DTC P0763 is a type A DTC.

Conditions for Running the DTC
^ The components are powered and ignition voltage is greater than 9 V and less than 18 V.
^ Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.

Conditions for Setting the DTC
DTC P0763 sets when the TCM detects any one of the following conditions:
^ An open circuit for 50 milliseconds.
^ A short to ground for 50 milliseconds.
^ A short to power in Solenoid C circuit for 50 milliseconds.

Action Taken When the DTC Sets
^ When in a forward range, the transmission will shift to another forward range while diagnostic response is active.
^ If the shift selector is moved to NEUTRAL, then the transmission will shift to NEUTRAL.
^ If the shift selector is moved to REVERSE, then the transmission will shift to NEUTRAL or REVERSE.
^ If the shift selector is returned to a forward range and the transmission is compromised by overspending or direction change, then the transmission will lock in NEUTRAL.
^ DTC P0763 will be stored in the TCM history.
^ The TCM freezes ship adapts (DNA).
^ Illuminates the MIL when active.
^ TCM inhibits TCC engagement.

Conditions for Clearing the MIL/DTC
A scan tool can clear the code 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. 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
^ When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
^ You may have to drive the vehicle in order to experience a fault.
^ Solenoids are sensitive to battery voltage spikes --cl poor ground connections. This condition might not be indicated with your Scan Tool, or even with a DVOM. The ideal way to test for these conditions would be to attach an oscilloscope.
^ If this DTC appears to be temperature-related, suspect a defective solenoid. A failing solenoid may be temperature sensitive causing resistance values to fluctuate.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests ignition voltage.
3. This step tests the command signal from the TCM, and tests for wiring harness for open/shorts.
4. This step tests the resistance value of the external harness and solenoid.
5. This step tests the command signal from the TCM.
6. This step tests the resistance value of the solenoid, and tests the internal wiring harness for open/shorts.
8. This step tests the resistance value of the solenoid.