Allison 3000 & 4000 Gen 4 Fault Code: P2808 Pressure Control Solenoid 6 (PCS6) Stuck Off


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 on-coming clutch controlled by Pressure Control Solenoid 6 (PCS6) engages during a forward range shift. PCS6 controls the C6 clutch for Low range in 3700/4700/4800 transmission models. PCS6 controls C6 clutch for Reverse 2 in the 4700/4800 model.

1. Hydraulic system is pressurized.
2. Hydraulic default condition not present.
3. Output speed is above 125 rpm.
4. Turbine speed above 60 rpm.
5. Engine initialization or shutdown is not in process.

DTC P2808 sets when the TCM detects the on-coming clutch did not maintain engagement after 2 seconds during the range shifts that require PCS6 to control C6 clutch.

When DTC P2808 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 diagnostics 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).

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.

NOTE: This DTC requires Clutch Test using the 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. High Main Mod commanded pressures correlate to no reduction in main pressure and clutch pressures. Refer to First Steps and Tips for Troubleshooting and 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 P2808 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 (SSI) low side solenoid wire (W151) may cause this code. There may be a P0973 in history with this code. SS1 strokes he 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. PCS6 controls the C6 clutch. However, this code may also occur when any other clutch did not maintain engagement while C6 is commanded.