Allison 1000 & 2000 Gen 5 Fault Code:P0880 TCM Power Input Signal

CIRCUIT DESCRIPTION:
The TCM requires a switched ignition voltage input and a direct battery voltage input. Battery direct voltage is supplied to pins 10 and 70 at the 80-way connector. DTC P0880 sets during the next ignition cycle if battery power is lost before the power down process is complete and the engine is running.

ACTION TAKEN WHEN THE DTC SETS:
When the DTC P0880 is active, the following conditions occur:
1. The CHECK TRANS light is not illuminated (non-OBD II strategy).
2. The DTC is stored in TCM history.
3. The TCM loses adaptive information for the drive cycle.
4. TCM reverts to previous adaptive settings.

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 the DTC recurring.

DIAGNOSTIC AIDS:
The following procedures are not documented in any OEM procedures or in any OEM Troubleshooting or Service information and should not be used as a method to diagnose any transmission DTC’s, function, or shift quality concern:

1.Back-probing any connections used for transmission features or functions may damage and/or unlock terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J-39700 Breakout Box, the appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

2. Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use J-39700 Breakout Box and appropriate harnesses with the diagnostic tool to monitor the circuit performance in question unless otherwise specified in the various Troubleshooting information.

3. Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

Inspect the wiring for poor electrical connections at the TCM. Look for the following conditions:
1. A bent terminal.
2. A backed-out terminal.
3. A damaged terminal.
4. Poor terminal tension
5. A chafed wire.
6. A broken wire inside the insulation.

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.