My Allison TCM still has no communication after being rebuilt.

If the TCM was repaired by us and programmed specifically to your VIN however upon getting your unit back you still have no communication chances are that there is something going on with the vehicle and most likely the wiring harness.

Check the harness for any poor grounding, and good connectivity (guide attached) and if the TCM is still not communicating then that would point to something with the TCM. We make sure a refurbished TCM is fully communicating on our bench test after repairs.

Also, make sure perform a hard battery reset once more to see if the connection with the TCM is re-established. Make sure the TCM is plugged in and then proceed with the hard reset.

If you're still having issues with your TCM after it has been refurbished. Here are some general tips to help you further troubleshoot the issue:

First, check that the vehicle's car battery is fully charged and getting a good connection.
Check the fuses.
Inspect the pins on both the harness plug as well as the TCM and make sure the pins are not pushed back on the harness plug. If some of the tabs are broken on the TCM plug the harness will have to be manually pushed in further towards the TCM to ensure a good connection.
Clean the pins with electronic cleaner on both the harness plug as well as the TCM itself and inspect for any dirty or receding pins.
Check the transmission fluid. If it's very dark and the filter is full of debris, it'll show trouble codes and the A/T along with the check engine light might come on. This is highly likely if the transmission fluid was never serviced and the vehicle has over 75,000 miles.

Perform a hard battery reset with the TCM plugged back into the vehicle to clear any remaining codes and reset the TCM:

Remove the key from the ignition.
With the battery removed, to ensure there is no power, short the battery cables in the vehicle and connect the positive and negative cables together for at least 20-30 minutes.
Reconnect the battery cables starting with the positive cable on the battery first.

This will reboot all the computer modules including the TCM and make the vehicle relearn its own values.

It's recommended to have the vehicle idle for a few minutes then take it for a drive at least 15-20 minutes after the hard battery reset.

It might idle rough at first and shift strangely but it should smooth out after the drive.

If you're not confident in doing the hard battery reset, simply leave the car battery disconnected overnight. The main goal is to drain the voltage in the computer modules to reboot them.

Troubleshoot 'No Communication' by using a multimeter, and check that there is continuity between the battery and the pins on the harness plugs. Testing the wiring harness pins for any connectivity issues:

For any communication issues, with the ignition-on, make sure that you do an ohm test between pins 6 and 27 on the harness plug for any remaining U0100 and U0101 (no communication) issues that are still present after the repair. There should be 120-ohm resistance.

If there is no ohm resistance present when you test between pins 6 & 27 then the issue is not the TCM. Check the pins and wiring all the way to the OBDII connector pinout.

Check the wiring harness for any pinched or torn wiring, check & clean the connector pins on the harness plug, and inspect closely with a flashlight for any corrosion or receding pins.

Pin 6 on the TCM plug should have continuity to Pin 6 on the OBDII connector under the dash driver-side. Pin 27 on the TCM plug should have continuity to Pin 14 on the OBDII connector.