Allison 3000 & 4000 Gen 4 Fault Code: P0977 Shift Solenoid 2 (SS2) Control Circuit High

DIAGNOSTIC RESPONSE:
7-speed: Allow 2 through 6, N, R

CIRCUIT DESCRIPTION:
The Shift Solenoid 2 (SS2) may either be assigned to retarder models with an air solenoid or to the SS2 required in 7-speed models. For retarder models with an accumulator, the Transmission Control Module (TCM) commands SS2 ON to enable the normally closed air solenoid which allows air pressure to stroke the accumulator piston to pre-fill the retarder cavity during retarder operation. For 7-speed models, the TCM commands the SS2 solenoid ON to send main pressure to both the C2 latch valve and the C6 interlock valve. The TCM sends control current to the solenoid from the High Side Driver 3 (HSD3) through wire 131. HSD3 is continuously ON unless the TCM detects a fault condition. Wire 119 completes the circuit between the solenoid and the TCM low side driver for SS2. The TCM energizes the solenoid by switching the solenoid’s low side driver ON. DTC P0977 indicates that the TCM has detected a failed high condition in the SS2 solenoid electrical circuit. The failed high condition may exist in the high side (wire 131) or low side (wire 119).

CONDITIONS FOR RUNNING THE DTC:
TCM initialized normally and engine speed above 200 rpm.

CONDITIONS FOR SETTING THE DTC:
This DTC sets when the TCM detects SS2 low side driver has been detected in a failed high state.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0977 is active:
1. For 7-speed models, limit ranges to Reverse (R) and ranges 2-6 operation.
2. TCM commands retarder OFF.
3. The TCM inhibits TCC engagement.
4. DTC is stored in the TCM history.
5. The CHECK TRANS light illuminates.
6. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P0977 can be caused by:
1. SS2 (7-speed only) issues such as:
– W119 shorted to another wire in chassis harness.
– W119 (terminal 17 of 20-way) shorted to another wire in internal transmission harness.
2. Air solenoid (SS2) issues such as:
– W119 shorted to another wire in chassis harness.
3. Defective air solenoid (SS2).
4. Broken of defective connector assemblies allowing pushed back pins to short together.
5. Unlocked connectors, missing seal plugs allowing moisture in connectors.
6. Defective TCM.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.