Allison 1000 & 2000 Gen 5 Fault Code:P071A Neutral At Stop Input Failed On

CIRCUIT DESCRIPTION:
When Neutral at Stop is active, the TCM automatically commands transmission operation at a reduced load state similar to Neutral (N). The purpose of the function is to reduce the load on the engine when the vehicle is stopped which improves fuel economy and also reduces heat load of the transmission in high start/stop duty cycles. To activate Neutral at Stop, the vehicle must be in first range, at a stop, service brakes applied, accelerator pedal approximately at 0%, and the TCM GPI terminal for Neutral at Stop must see V+, V Ign, or V Bat. Neutral at Stop deactivates when the service brake is released. Supplemental controls such as a door switch or a Neutral Stop enable dash switch may be wired in series with the service brake pressure switch or, alternately, a vehicle Programmable Logic Controller (PLC) output may switch the Neutral at Stop signal as a result of a service brake pressure switch input to the PLC. The signal used to activate Neutral at Stop is W143, depending upon which Input/Output (I/O) package was selected in the TCM calibration. Neutral at Stop typically uses a switch-to-battery input (analog). Refer to the OEM Technician Library for Neutral at Stop wiring information. The test monitors whether the Neutral at Stop input status is in a stuck “ON” or “OFF” state.

Neutral at Stop:
GPI#: 3
GPI Type: +
TCM Pin Number: 43
Wire Number: 143
Wire Color: Blue
Termination Point(s): Service Brake Pressure Switch to V+ or PLC Output

ACTION TAKEN WHEN THE DTC SETS:
When DTC P071A is active, the following conditions occur:
1. The DTC is stored in the TCM history.
2. The TCM does not illuminate the CHECK TRANS light.
3. TCM inhibits Neutral at Stop operation.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
The diagnostic tool may be used 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:
This DTC may be caused by:
1. Short to power or short to another wire for the GPI circuit controlling Neutral at Stop feature, i.e., W143.
2. For service brake integrations, defective switch or incorrect wiring, e.g., pressure switches are closed when they should be open. If Neutral at Stop enable switch or door switch integrated in series, all switches would need to be stuck closed or wired on wrong side of switches, e.g., normally closed side vs normally open side.
3. For PLC Neutral at Stop integrations, a miswired, misprogrammed, or defective circuit from PLC controlling the TCM GPI signal for Neutral at Stop that is maintaining circuit above 3.4 volts with service brakes released.
4. Neutral at Stop enabled in TCM programming in error.
5. TCM ground is at different voltage potential than the ground of the OEM voltage source responsible for switching GPI circuit controlling Neutral at Stop, e.g. PLC, vehicle ignition, body controller, etc.
6. Defective TCM.

NOTE: The OEM transmission warranty, or the extended coverage for parts and labor, does not cover the repair or replacement of OEM or body builder provided components or any external wire harnesses not provided by the OEM.

Before repairing or replacing these components or circuits that caused a transmission issue, always contact the vehicle OEM call center and/or the vehicle OEM or bodybuilder service representative to verify the warranty coverage and proper payment arrangements, arrange an alternate sublet or repair plan (if needed), and get troubleshooting assistance for the repair (such as vehicle schematics, DTC trees, parts assistance, etc).