Eaton UltraShift Plus intermittent F (Fault) - J1939 Link Loss

Question

Running a 2016 Kenworth and the Eaton transmission keeps dropping into 'F' on the gear display and won't shift out of neutral when starting in the morning. Sometimes it happens while cruising and the truck just loses throttle response until I cycle the key. I am seeing code 81 on the transmission controller tool which points to a communication failure.

road_rambler · Accepted Answer

The issue was a corroded OEM 9-pin pass-through connector at the firewall bulk-head. Pin C and D had significant oxidation which was dropping the voltage on the J1939 signal intermittently. I bypassed the bulkhead connector using a Deutsch HD10 series 2-pin connector and verified the resistance stayed at 60 ohms while shaking the harness. Cost was about $45 in parts and 3 hours of diagnostic time.

garagegrease · Answer

Code 81 is almost always a physical layer issue on the J1939 backbone. Check the terminating resistors; you should see 60 ohms across CAN High and CAN Low with the batteries disconnected. If you see 120 ohms, one of your resistors is dead or the circuit is open.

Megan Rivera · Answer

Make sure your Engine Control Module and Trans Control Unit are on the same software revision levels. Sometimes a mismatch after an ECM replacement causes timeout errors that trigger a link loss fault.

fleet_chief_42 · Answer

I've seen this happen when the heavy wiring harness rubs against the back of the flywheel housing. Look for a green crusty spot in the harness where the twisted pair for the J1939 might be shorting to ground or each other.

Eaton UltraShift Plus intermittent F (Fault) - J1939 Link Loss

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