Allison 3000 & 4000 Gen 4 Fault Code: P0881 TCM Power Input Signal Performance

DIAGNOSTIC RESPONSE:
None

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) requires direct battery voltage input to operate. This test monitors for low or excessive swings in battery voltage to the TCM on terminals 10 and 70.

NOTE: The TCM battery power signal must be provided through a 10A or 15A fuse, or a manually-reset circuit breaker.

CONDITIONS FOR RUNNING THE DTC:
1. Engine speed above 500 rpm or more for at least 1.5 seconds.
2. DTC test runs at 0.50 second intervals.

CONDITIONS FOR SETTING THE DTC:
DTC P0881 sets when the TCM detects battery voltage is less than 9 volts after engine runtime over 30 seconds.
1. The TCM detects direct battery voltage below 6.5V for longer than 3 seconds with engine speed above 500 rpm.
2. The TCM detects a battery voltage swing of 6V or more for longer than 0.5 seconds with engine speed above 500 rpm.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM illuminates the CHECK TRANS light.
2. TCM may not reset if ignition is turned OFF.
3. Solenoids OFF (Hydraulic default).
4. TCC solenoid OFF.
5. Main Mod solenoid OFF.

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:
1. A defective vehicle battery may allow this DTC to set. Test all vehicle batteries to OEM specifications for proper voltage and load capacity.
2. A defective vehicle charging system may cause this DTC. Test the charging system to all OEM specifications. Low voltage or electrically noisy alternators may prevent clean or ample battery voltage from reaching the TCM. If alternator performance is preventing clean battery power on the vehicle, consider using the alternate ignition power diagram shown in OEM Tech Data.
3. Battery voltage is available on the diagnostic tool Data Monitor grid. Prior to ‘Connect’ for the diagnostic tool, check the ‘Troubleshoot Specific Problem’ box under “Connection Options” and then check the ‘Sensor, Voltage, Ohms, and Counts Data’ box.
4. Disconnecting battery power (e.g., via master disconnect) before switching OFF ignition power may cause this DTC. Direct battery power must be maintained for at least 2 to 3 seconds after ignition is switched OFF.
5. Broken or defective connector assemblies allowing pushed back pins to short together.
6. Unlocked connectors, missing seal plugs allowing moisture in connectors.
7. Defective TCM may cause this code.

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