Allison 1000 & 2000 Gen 5 Fault Code:P0777 Pressure Control Solenoid 2 (PCS2) – Stuck On

CIRCUIT DESCRIPTION:
Pressure Control Solenoid 2 (PCS2) controls 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. DTC P0777 sets when the TCM detects an incorrect oncoming ratio (range-to-range) for an accumulated number of occurrences.

The TCM uses information from the turbine and output speed sensors to detect if a clutch is in a tie-up condition or if three clutches are applied. The clutch being controlled by PCS2 varies depending on the shift.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0777 is active, the following conditions occur:
1. If failure occurs while in a forward range, the transmission shifts to the previous range.
2. If failure occurs while in N (Neutral) or R (Reverse), the transmission locks in N (Neutral).
3. If the shift selector is moved to N (Neutral), the transmission shifts to N (Neutral) (some cases may lock in N (Neutral)).
4. If the shift selector is moved to R (Reverse), the transmission shifts to R (Reverse) or N (Neutral).
5. If the shift selector is returned to a forward range and the transmission is compromised by overspeeding or a direction change, the transmission will shift to N (Neutral).
6. DTC is stored in TCM history.
7. The CHECK TRANS light illuminates (non-OBD II strategy).
8. The TCM forces Variable Modulated Main off.
9. TCM inhibits Torque Converter Clutch (TCC) engagement.
10. TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic 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 the DTC recurring.

DIAGNOSTIC AIDS:
This DTC indicates the off-going clutch being controlled by PCS2 is not applied or is released too slowly. This could indicate a leak or obstruction in a specific clutch apply circuit. Check the diagnostic 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 information to determine which clutch circuit is suspect.

If the condition is intermittent, connect the diagnostic tool and select the speed sensor indicated by the DTC. If the signal is erratic, investigate and eliminate the following:
1. Intermittent wiring connection.
2. Excessive vibration (driveline or engine torsionals).
3. Irregular sensor gap (loose sensor, loose tone wheel, or damaged tone wheel).

Inspect and confirm that the OEM engine rating does not exceed the transmission model rating. Also inspect for the presence of an add-on engine power package or module. Whenever the engine horsepower or torque is increased over the transmission factory rating, a shift flare condition may occur leading to the DTC indicated.

NOTE: Clutch failure due to an OEM engine rating exceeding the OEM transmission rating, or the installation of an engine power package or module will not be covered under the OEM transmission warranty.