Allison 3000 & 4000 Gen 4 Fault Code: P088B Transmission Filter Maintenance Required

DIAGNOSTIC RESPONSE:
None

CIRCUIT DESCRIPTION:
The Filter Life Monitor (FM) feature alerts the driver when a filter change is needed by illuminating the SERVICE TRANS indicator (wrench icon in keypad or lever shift selector display). FM also activates any OEM-provided SERVICE TRANS indicator or datalink message center display (when integrated to receive the message). If the filter is detected as restricted, the wrench icon in the selector flashes ON and OFF for approximately 2 minutes the first time D (Drive) is selected after each engine start. Also, DTC P088A becomes active concurrently with these other visible filter maintenance alerts. This DTC monitors the electrical state of the PS2 Filter Life Indicator (FLI) pressure switch. If PS2 is detected as open (pressurized) while the transmission is in a forward range and with the Torque Converter Clutch (TCC) (lockup) solenoid energized, the DTC becomes active. If several alerts are sent, but the PS2 switch is still detected as pressurized, DTC P088B becomes active.

The difference between main pressure (before the filter) and TCC lockup pressure determines whether to stroke or de-stroke the FLI pressure switch valve in the prognostics valve body within the control valve module.

An active DTC and SERVICE TRANS indicator occurs at next engine start when the operator selects D (Drive).

ACTION TAKEN WHEN THE DTC SETS:
1. DTC P088B is stored in the TCM history for a number of ignition cycles.
2. The wrench icon in the display of a shift selector will flash ON and OFF for approximately 2 minutes the first time D (Drive) is selected after each engine start.
3. The TCM illuminates the CHECK TRANS light.

CONDITIONS FOR CLEARING THE DTC:
1. The feature is designed to reset itself automatically after the main filter has been changed.
2. The diagnostic tool can clear the DTC from TCM history.
3. The operator may clear the code and flashing SERVICE TRANS indicator by pressing the MODE button for 10 seconds provided the CMC to disable a reset from the shift selector was not enabled. However, if the filters are not changed, the DTC will most likely become active again.
4. FM may also be reset by selecting N-R-N-R-N-D-N on the shift selector, pausing briefly (less than 3 seconds) between each selector movement when the ignition is on and the engine not running.
5. FM may be reset with a SAE J1939 message.
6. 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:
Refer to the OEM 4th Generation Control System Operation and Prognostics Package and Features for important information about Oil Life Monitor (OM), FM, and Transmission Health Monitor (TM). These sections discuss prognostics principles of operation, feature requirements, maintenance alerts, reports, and processes to reset features or change fluid type (January 2010 and later TCM software) using either the diagnostic tool or an OEM-supplied shift selector.

The diagnostic tool will show PS2 PRESSURIZED when PS2 is open and PS2 EXHAUSTED when PS2 is closed.

DTC P088B can be caused by:
1. Restricted Main Filter.

NOTE: Change both main and lube filters if main filter is restricted.

2. Low lockup pressure.
3. Open or high resistance in W118 or W158 in chassis harness.
4. Open or high resistance from terminal 17 to PS2, or from PS2 to terminal 19, in control module wire harness.
5. Issue with PS2.
6. Issue with TCM.