Allison 3000 & 4000 Gen 4 Fault Code: P0894 Transmission Component Slipping

DIAGNOSTIC RESPONSE:
DNS, Lock in first

CIRCUIT DESCRIPTION:
This DTC test detects if the expected turbine speed pull-down did not occur or the expected gear ratio was not attained during the TCM range attained verification check.

CONDITIONS FOR RUNNING THE DTC:
1. Hydraulic system is pressurized.
2. Hydraulic default condition not present.
3. Output speed is above 60 rpm (20 rpm for Reverse 2 (R2)).
4. Engine initialization or shutdown is not in process.
5. Engine speed above 800 rpm.
6. Shifting complete.
7. Range attained is not Neutral (N).
8. Reverse-to-Neutral shift not in process.
9. For fire truck applications, pump is not pumping.

CONDITIONS FOR SETTING THE DTC:
DTC P0894 sets if detected output speed is less than TCM target value for output speed during TCM range attained verification.

ACTION TAKEN WHEN THE DTC
When DTC P0894 is active, the following conditions will occur:
1. Lock in range.
2. The CHECK TRANS light illuminates.
3. DTC is stored in the TCM history.
4. TCM inhibits TCC engagement.
5. TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
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:
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. 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 therefore clutch pressures). Refer to First Steps and Tips for Troubleshooting and 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 P0894 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.