Allison 3000 & 4000 Gen 4 Fault Code: P0880 TCM Power Input Signal

DIAGNOSTIC RESPONSE:
No

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) requires direct battery voltage input to operate. This test detects abnormal power down of battery voltage to the TCM on terminals 10 and 70 with ignition sense ON.

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 350 rpm for at least 0.5 seconds,
2. DTC test runs at after each normal TCM initialization or after TCM reset.

CONDITIONS FOR SETTING THE DTC:
DTC P0880 sets during the next ignition cycle if battery power is lost before the power down process is complete. Normal power down of the TCM takes 2 to 3 seconds after ignition switch input W163 is switched OFF. The selector stays illuminated during this 2 to 3 second process as power OFF data, such as adaptive information, is saved to memory.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM does not illuminate the CHECK TRANS light.
2. TCM may not reset if ignition is turned OFF.
3. TCM reset.

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.
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 is a common cause for this DTC. Direct battery power must be maintained for at least 2 to 3 seconds after ignition is switched OFF.
5. Defective TCM may cause this code.

NOTE: If a DTC with either a ‘lock in range’ or ‘shift to alternate range’ response was present during the previous power cycle and a DTC P0880 is detected during TCM initialization, the TCM will not complete initialization. An incomplete TCM initialization is indicated by a specific behavior of the shift selector; (i.e. the shift selector will illuminate all segments in the shift display for 12 or more seconds.) The TCM may still be checked for code history using the diagnostic tool at this time as long as power has been restored to the TCM. Use the troubleshooting manual to troubleshoot stored DTCs that are present during the incomplete TCM initialization.

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