P0747

ALLISON AUTOMATIC TRANSMISSION

DTC P0747
Circuit Description for Allison Automatic Transmission
Pressure control (PC) solenoid A is used to control oncoming, off-going, and holding pressure to any one of the five clutches. This solenoid is referred to as a pressure proportional to current (PPC) solenoid since the output hydraulic pressure supplied by this solenoid is proportional to the controlled current command.

The transmission control module (TCM) uses information from the turbine and output speed sensors to detect if a clutch is in a tie-up condition or 3 clutches are applied. The clutch being controlled by PC solenoid A will vary depending on the shift being made.

DTC P0747 is a type A DTC.

DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0747 Pressure Solenoid A Stuck On

Conditions for Running the DTC
^ DTCs P0716, P0717, P0721, P0722, P0875, and P0876 are not active.
^ The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
^ Output speed is greater than 200 RPM.
^ Turbine speed is greater than 200 RPM.

Conditions for Setting the DTC
DTC P0747 sets if the TCM determines off-going clutch controlled by PC solenoid A remains engaged during a forward range shift.

Action Taken When the DTC Sets
^ The TCM illuminates the malfunction indicator lamp (MIL).
^ When failure occurs in a forward range, the transmission will go to the previous range. If failure occurs in NEUTRAL or REVERSE, the transmission will lock in NEUTRAL while diagnostic response is active.
^ If the shift selector is moved to NEUTRAL, the transmission will shift to NEUTRAL.
^ If the shift selector is moved to REVERSE, the transmission will shift to REVERSE or NEUTRAL, or in some cases may lock in NEUTRAL.
^ If the shift selector is returned to a forward range and the transmission is compromised by over speeding or direction change, the transmission will shift to NEUTRAL.
^ DTC P0747 will be stored in TCM history.
^ The TCM freezes shift adapts.
^ The TCM inhibits torque converter clutch (TCC) engagement.

Conditions for Clearing the DTC
A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids
^ Inspect the wiring for poor electrical connections at the TCM. Inspect 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 condition.
^ This DTC indicates the off-going clutch being controlled by PC solenoid A, is not releasing or is slow to release. This could indicate a leak or obstruction in a specific clutch apply circuit. Observe scan tool failure record data for previous or current range information when the DTC was set, to determine the specific shift when the DTC was set. Refer to Solenoid and Clutch Chart to determine which clutch circuit is suspect. Allison - Automatic Transmission

^ Important: Clutch failure due to installation of an engine power upgrade is not covered under the manufacturers warranty.

Inspect for the presence of an add-on engine power package. When engine horsepower or torque is increased over factory rating, a shift flare condition may occur.

Test Description








The numbers below refer to the step numbers on the diagnostic table.
3. This step tests for proper ignition voltage.
4. This step tests for erratic speed sensor readings.
5. This step tests for internal hydraulic leakage.
6. This step tests for clutch capacity.