How to Resolve Allison 3000 & 4000 Gen5 Transmission P071A Neutral at Stop Input Failed ON

This guide provides step-by-step instructions on diagnosing and resolving the P071A Neutral at Stop Input Failed ON issue in Allison 3000 & 4000 Gen5 transmissions.

Understanding the Neutral at Stop Function

Circuit Description

When the Neutral at Stop function is active, the Transmission Control Module (TCM) automatically shifts the transmission to a reduced load state similar to Neutral (N) when the vehicle is stopped. This feature:

Improves fuel efficiency
Reduces heat buildup during frequent stop/start operations

For activation, the following conditions must be met:

Vehicle in first range
Vehicle completely stopped
Service brakes applied
Accelerator pedal at 0%
TCM GPI terminal for Neutral at Stop detects V+, V Ign, or V Bat

Deactivation Conditions

Neutral at Stop disengages when the service brake is released. Additional controls, such as a door switch or dashboard switch, may also be used in series with the service brake pressure switch.

The input signal to activate Neutral at Stop may be located on W102, W123, or W143, depending on the I/O package selected in the TCM calibration. This function typically uses a switch-to-battery input (analog).

For further details, refer to the OEM Technician’s Library.

Neutral at Stop Wiring Details

GPI #	GPI Type	TCM Pin	Wire #	Wire Color	Termination Point
1	+	23	123	Green	Service Brake Pressure Switch to V+ or PLC Output
2	+	2	102	Yellow	Service Brake Pressure Switch to V+ or PLC Output
3	+	43	143	Blue	Service Brake Pressure Switch to V+ or PLC Output

What Happens When DTC P071A Sets?

When DTC P071A is active, the following occurs:

The DTC is stored in the TCM history.
The CHECK TRANS light does not illuminate.
TCM disables the Neutral at Stop function.

How to Clear the DTC / CHECK TRANS Light

Use a diagnostic tool to clear the DTC from the TCM history.
The TCM will automatically clear the DTC after 40 successful warm-up cycles without the issue recurring.

Diagnostic Aids: Common Causes of P071A

1. Electrical Short or Wiring Issues

Short to power or short to another wire in the Neutral at Stop GPI circuit (W102, W123, or W143).

2. Service Brake Integration Issues

Defective brake switch or incorrect wiring (e.g., pressure switches staying closed when they should be open).
If additional switches (e.g., Neutral at Stop enable switch or door switch) are wired in series, they may be stuck closed or miswired.

3. PLC (Programmable Logic Controller) Integration Issues

Incorrect wiring, programming, or faulty circuit in the PLC controlling the TCM GPI signal.
If the PLC maintains the circuit above 3.4 volts when the service brakes are released, the issue may persist.

4. TCM Programming Errors

Neutral at Stop function may have been incorrectly enabled in the TCM settings.

5. Voltage Potential Differences

TCM ground voltage differs from the OEM voltage source responsible for switching the GPI circuit (e.g., PLC, vehicle ignition, body controller).

6. Defective TCM

If all other diagnostics check out, the TCM itself may be faulty.

By following this guide, you can diagnose and fix the P071A issue to restore the Neutral at Stop functionality in Allison 3000 & 4000 Gen5 transmissions.

More Allison repair case,please refer to Allison Trouble Repair

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