Allison 1000 & 2000 Gen 5 Fault Code:P0961 Main Pressure Modulation Solenoid System Performance

CIRCUIT DESCRIPTION:
Main Pressure Modulation Solenoid is a normally closed solenoid that regulates main pressure to allow for decreased engine loading. The intent of this code is to ensure that the Main Pressure Modulation Solenoid defaults to full pressure if a clutch slip event occur. This response is designed to help protect the transmission from internal clutch damage due to low main pressure. DTC P0961 sets when the Main Pressure Modulation Solenoid is on and the number of slip events for a range is equal to or greater than a calibrated number of counts, and gear slip is indicated.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0961 is active, the following conditions occur:
1. The CHECK TRANS light illuminates (non-OBD II strategy).
2. Variable Modulated Main pressure is disabled, allowing full main pressure to be implemented.
3. The DTC is stored in the TCM history.

CONDITIONS FOR CLEARING THE DTC:
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:
1. You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time, etc. This data can be useful in reproducing the failure mode when the DTC was set.
2. Do not run the vehicle for extended periods of time with this DTC active or transmission overheating may occur.
3. If the transmission has had the transmission fluid changed, is low, or had the Control Module removed and replaced, this DTC can be set. Clear code. Check for proper transmission fluid level and verify that the code returns.
4. This DTC could indicate a cut clutch seal, damaged clutch, or defective main modulation solenoid.
5. Incorrect ratio codes typically indicate mechanical problems with specific clutches for range indicated; for example, C1 and C5 for 1st range.
6. An incorrect ratio DTC may indicate a mechanically failed clutch.
7. Output or turbine tone wheel damage may cause erratic speed sensor input allowing this DTC to set.