Allison 3000 & 4000 Gen 4 Fault Code: P2724 Pressure Control Solenoid 1 (PCS1) Stuck On

DIAGNOSTIC RESPONSE:
DNS, RPR

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) uses input from the turbine speed and output speed sensors to determine the current commanded for steady-state gear ratio. The TCM then compares the known gear ratio to the calculated gear ratio for the current range.

This DTC test determines if the off-going clutch controlled by Pressure Control Solenoid 1 (PCS1) remains engaged during a forward range shift. PCS1 controls the C1 clutch for 1st through 4th gears in all 3000 and 4000 transmissions, and the Low range in 4700/4800 transmissions. PCS1 does not control clutches for Low range in the 3700 transmission.

CONDITIONS FOR RUNNING THE DTC:
1. Hydraulic system is pressurized.
2. Hydraulic default condition not present.
3. Output speed is 200 rpm or higher.
4. Turbine speed is 200 rpm or higher.
5. Engine initialization or shutdown is not in process.

CONDITIONS FOR SETTING THE DTC:
DTC P2724 sets when the TCM detects the off-going clutch did not fully release after 2 seconds during the range shifts that require PCS1 to control C1 clutch.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2724 is active, the following conditions will occur:
1. If DTC goes active while making a forward range shift (e.g., 1-2), the transmission returns to the previous range. If DTC goes active during a shift to reverse or neutral, the transmission shifts to neutral. Once shifting is complete, the attained range is locked in range.
2. While diagnostic response is active, the TCM ignores shift selector inputs.
3. The CHECK TRANS light illuminates.
4. DTC is stored in the TCM history.
5. TCM inhibits TCC engagement.
6. TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:/CHECK
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
NOTE: This DTC requires Clutch Test using diagnostic tool to detect clutch slip during a partial stall and also to pressurize clutches for measurement without needing to drive the vehicle. Note that main pressure and clutch pressures are reduced when the Main Mod Solenoid is energized. Low commanded Main Mod solenoid pressures shown in Data Monitor correlate to reduced main pressure and clutch pressures. Main pressure is reduced by Main Mod in N (Neutral), 1 (First Range), and 2 (Second Range) when engine speed is below 1500 rpm. Higher Main Mod commanded pressures correlate to no reduction in main pressure and clutch pressures. Refer to First Steps and Tips for Troubleshooting and refer to the OEM Technician’s Library for more information about the action requests for Clutch Test, Full Main Pressure Test, and also the procedure for Stall Testing.

DTC P2724 may be caused by:
1. Output speed sensor signal circuit issues.
2. Turbine speed sensor signal circuit issues.
3. Low clutch pressures, main pressure, or control main pressure.
4. Control module issues like stuck/sticky valves, mechanically defective solenoids, broken springs, damaged valve bores, plugged suction filter, damaged gaskets, excessive leaks to exhaust, etc.
5. Transmission issues such as damaged output speed sensor wheel slot, worn and/or damaged seals or seal rings, dislocated snap rings, worn clutch packs, rotating drum damage (affecting turbine speed pickup), debris, excessive hydraulic circuit leaks to exhaust or other hydraulic circuits.

NOTE: Damage to the output speed sensor wheel slot is an indication the driveline does not meet ATI specifications. Correct all driveline issues before putting transmission back in service.

6. Issue with TCM.
7. A high resistance circuit in Shift Solenoid 1 (SS1) low side solenoid wire (W151) may cause this code. There may be a P0973 in history with this code. SS1 strokes the C2 latch valve when energized. A high resistance connection may not fully energize the SS1 in order to stroke the C2 latch. Check for expanded terminals, broken/loose connectors, loose pin crimps, or damaged W151 in chassis harness. Check condition of wire harness in control valve module and the SS1 resistance if needed.
8. PCS1 controls the C1 clutch. However, this code may also occur for any off-going clutch issue while C1 is commanded.