Allison 3000 & 4000 Gen 4 Fault Code: P0657 Actuator Supply Voltage 1 (HSD1) Open

DIAGNOSTIC RESPONSE:
SOL OFF, DNA, Inhibit TCC operation, Inhibit main modulation

CIRCUIT DESCRIPTION:
The high side drivers are connected to the high side circuits of the solenoids and commanded on during normal operation. The high side drivers serve as a master switch to supply battery voltage to the low side drivers. High side drivers are turned on during TCM initialization and remain on during normal operation. High side drivers are turned off during cranking and for certain diagnostic responses. The open circuit diagnostic is determined by monitoring the status of the low side drivers. If two or more of the low side drivers circuits are detected by the TCM in a failed open/low state that are supplied by a particular high side driver circuit, the problem is assumed to be on the high side of the load and a high side driver fault becomes active instead of two or more low side driver faults becoming active. There may or may not be low side driver faults present with this DTC. High Side Driver 1 (HSD1) supplies battery voltage to the Main Mod, Pressure Control Solenoid 4 (PCS4) and Pressure Control Solenoid 6 (PCS6) via wire 111. The TCM regulates control current to the solenoids by switching the appropriate low side driver on and off.

CONDITIONS FOR RUNNING THE DTC:
1. DTC enabled with ignition ON, engine OFF, and battery voltage greater than 9 volts.
2. HSD1 is commanded ON.
3. DTC disabled while engine is cranking longer than 4 seconds, and while battery voltage is less than 10 volts.
4. DTC re-enabled once engine is running and TCM is initialized normally.

CONDITIONS FOR SETTING THE DTC:
This DTC sets when the TCM detects two or more low side drivers connected to HSD1, e.g., Main Mod, PCS4, or PCS6 (if enabled) low side drivers, have been detected in a failed low/open state while HSD1 voltage is greater than 6 volts.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0657 is active:
1. The DTC sets while in a forward range, then shifts to another forward range. If failure occurs while in Neutral (N). If failure occurs while in Reverse (R), the transmission remains in Reverse (R) or shifts to Neutral (N). Once range is attained, transmission is locked in this range and there is no response to shift selector requests.
2. The TCM inhibits TCC engagement.
3. Main Modulation is inhibited.
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 from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P0657 can be caused by:
1. HSD1 circuit issues such as:
– W111 shorted to another wire in chassis harness.
– W111 (terminal 1 of 20-way) shorted to another wire in the internal transmission harness.
– W111 open circuit in chassis harness.
– W111 (terminal 1 of 20-way) open circuit in internal transmission harness.
2. Two or more low side driver circuit issues with Main Mod, PCS4, or PCS6.
3. Main Mod issues such as:
– W174 shorted to another wire in chassis harness.
– W174 shorted (terminal 8 of 20-way) to another wire in the internal transmission harness.
– W174 open circuit in chassis harness.
– W174 (terminal 8 of 20-way) open circuit in internal transmission harness.
4. PCS4 issues such as:
– W155 shorted to another wire in chassis harness.
– W155 shorted (terminal 2 of 20-way) to another wire in the internal transmission harness.
– W155 open circuit in chassis harness.
– W155 (terminal 2 of 20-way) open circuit in internal transmission harness.
– PCS4 solenoid open or shorted.
5. PCS6 (7-speed only) issues such as:
– W178 shorted to another wire in chassis harness.
– W178 shorted (terminal 7 of 20-way) to another wire in the internal transmission harness.
– W178 open circuit in chassis harness.
– W178 (terminal 7 of 20-way) open circuit in internal transmission harness.
6. Defective solenoids Main Mod, PCS4, PCS6.
7. Unlocked connectors, expanded terminals, poor pin crimps or unlocked pins causing high resistance or open circuit.
8. Defective TCM.

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