Eaton UltraShift Plus - FMI 81 J1939 Engine Message Loss

Question

My 2016 Peterbilt 579 is stuck in neutral and won't initiate a gear. The dash is flashing an 'F' and my Eaton ServiceRanger is pulling a FMI 81 code saying the transmission has lost the J1939 communication link with the engine ECM.

Greg Walters · Accepted Answer

I found the issue was a green-crusty broken wire inside the OEM 38-way interface harness. The J1939 High wire (Yellow) had been chaffing against a plastic zip-tie about 6 inches back from the TECU connector. I cut back the harness, soldered in a new 3-inch section of twisted pair wire, and heat-shrunk the connection. Once the J1939 continuity was restored, the FMI 81 cleared immediately and the transmission went back into gear. Total cost was just the price of the solder and some new loom.

garagegrease · Answer

Check your terminating resistors. You should see 60 ohms across the CAN line at the diagnostic port with the batteries disconnected. If you see 120 ohms, you have a physical break in the backbone.

torque_terry · Answer

Verify the PACCAR ECM is actually sending the torque and speed messages. Sometimes a failing engine ECM won't broadcast on the V-CAN while the internal logic still seems to function for the engine itself.

Mike Reynolds · Answer

Check the 4-pin Diagnostic/Power connector at the transmission. Often the J1939 wires (yellow and green) rub through right where the harness curves over the top of the bellhousing.

Eaton UltraShift Plus - FMI 81 J1939 Engine Message Loss

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