Allison 3000 & 4000 Gen 4 Fault Code: P2671 Actuator Supply Voltage 2 (HSD2) High

DIAGNOSTIC RESPONSE:
DNS, SOL OFF (hydraulic default)

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. High Side Driver 2 (HSD2) supplies battery voltage to the Pressure Control Solenoid 1 (PCS1), Pressure Control Solenoid 2 (PCS2), Pressure Control Solenoid (PCS3), and Shift Solenoid 1 (SS1) via wire 171. The TCM regulates control current to the solenoids by switching the appropriate low side driver on and off. This test detects if the voltage measured at the HSD2 detection circuit indicates high during initialization when the circuit is off.

CONDITIONS FOR RUNNING THE DTC:
During TCM initialization while high side driver is commanded off.

CONDITIONS FOR SETTING THE DTC:
This DTC sets during TCM initialization, if HSD2 voltage detected to be greater than 6V while HSD2 circuit is OFF.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2671 is active:
1. Transmission fails to Neutral (N).
2. DTC is stored in the TCM history.
3. The CHECK TRANS light illuminates.
4. 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 P2671 can be caused by:
1. HSD2 circuit issues such as:
– W171 shorted to another wire in chassis harness.
– W171 (terminal 6 of 20-way) shorted to another wire in the internal transmission harness.
2. Two or more low side driver circuit issues with PCS1, PCS2, PCS3, or SS1.
3. PCS 1 issues such as:
– W136 shorted to another wire in chassis harness.
– W136 shorted (terminal 4 of 20-way) to another wire in the internal transmission harness.
4. PCS2 issues such as:
– W152 shorted to another wire in chassis harness.
– W152 shorted (terminal 5 of 20-way) to another wire in the internal transmission harness.
5. PCS3 issues such as:
– W133 shorted to another wire in chassis harness.
– W133 shorted (terminal 9 of 20-way) to another wire in the internal transmission harness.
6. SS 1 issues such as:
– W151 shorted to another wire in chassis harness.
– W151 shorted (terminal 10 of 20-way) to another wire in the internal transmission harness.
7. Broken or defective connector assemblies allowing pushed back pins to short together.
8. Unlocked connectors, missing seal plugs allowing moisture in connectors.
9. Defective TCM.

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