Allison 3000 & 4000 Gen 4 Fault Code: P2789 Clutch Adaptive Learning at Limit

DIAGNOSTIC RESPONSE:
None

CIRCUIT DESCRIPTION:
The Transmission Health Monitor is (TM) is part of the 4th Generation Control System Prognostics package. This feature monitors adaptively learned clutch volume changes. These volumes are correlated to calculated free running clearances for each of the transmission clutches C1, C2, C3, C4, and C5. The adaptive information is compared with the baseline volumes and clearances established by the function when the clutches were new or just after a function reset was performed following a clutch system repair.

If the predicted clutch life left for C1 through C5 is 6% or less, or if the predicted free running clearance of any clutch exceeds its maximum value, then the TRANS SERVICE indicator (wrench icon on Allison shift selector) illuminates informing the operator that there is a need for service. The wrench icon (and TRANS SERVICE indicator, if separate) stays illuminated during vehicle operation until clutch system service is performed and the TM function can reset itself with the new predicted values. The OEM may also be used to reset the TM function in the Action Request screen.

If the TM function is not reset within several ignition cycles of illuminating the TRANS SERVICE indicator, then a CHECK TRANS indicator illuminates indicating P2789. The TM automatically resets itself if the function detects that the values for remaining clutch life or predicted free running clearance are back within specification.

CONDITIONS FOR RUNNING THE DTC:
Enabled by calibration

CONDITIONS FOR SETTING THE DTC:
This DTC sets when percent clutch life remaining is less than 6% and continues to stay under 16% for the next 100 hours of TCM run time.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM illuminates the CHECK TRANS light.
2. The DTC is stored in the TCM history.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
1. This DTC goes inactive when percent clutch life remaining is predicted to be more than 16%.
2. Use the diagnostic tool to Reset Transmission Health Indicator by specific clutch(es) through the Action Request screen. The DTC may also be cleared from TCM history using the diagnostic tool.

DIAGNOSTIC AIDS:
Refer to OEM 4th Generation Control System Operation and Prognostics Package and Features for important information about Oil Life Monitor (OM), Filter Life Monitor (FM), and Transmission Health Monitor (TM). These sections discuss prognostics principles of operation, feature requirements, type of maintenance alerts, reports, and processes to reset features or change fluid type (available January 2010 and later TCM software) using both the diagnostic tool or an OEM-supplied MY09 and later shift selector.

Other factors besides clutch wear may cause this DTC such as:
1. OEM solenoid wiring issue, e.g., high resistance wires, poor pin crimps expanded terminal, poor power and grounds.
2. Defective solenoid.
3. Sticking valve.
4. Worn valve body.
5. Weak trim springs.
6. Low main pressure.
7. Low control main pressure.
8. Leak to sump of exhaust backfill.
9. Leaking piston seal.
10. Defective TCM.

NOTE: When transmission clutches are replaced, always select “Reset Adaptive Shift Parameters” and “Reset Prognostics Information” on the diagnostic tool. This will allow access to “Reset Transmission Health Monitor” and “Reset Oil Life Monitor” from the “Action Request” menu. Refer to Fluid Check Procedures, Prognostics Package and Features, First Steps and Tips for Troubleshooting, and the OEM Technician’s Library for additional information.

NOTE: Do not base transmission removal solely because this DTC is active or that a Trans Health report comes back red on a clutch. Instead, perform an inspection and function check of the transmission in chassis, if possible, e.g., clutch tests, pressure checks, and stall check to look for slipping clutch, etc. If the transmission function checks, such as fluid filter check, fluid condition check, shift quality check, and clutch pressure check are all normal, then do not remove the transmission from the vehicle. Instead, continue to monitor the transmission for issues and look for other causes for the high fill volumes mentioned in Diagnostic Aids for this DTC.

NOTE: Refer to General Troubleshooting of Performance Complaints for indicator lamp issues. OEM action requests and lamp tests may be used to check functionality of SERVICE TRANS indicator (wrench icon).