How to Fix / Troubleshooting

Safety first: Shut off power to both indoor and outdoor units before accessing control compartments.

Check wiring diagram: Locate the Trane wiring diagram on the service panel. Confirm that communication wires (often labeled D+, D-, or specific Trane terminals) are landed correctly and with correct polarity at both indoor and outdoor boards.
Inspect cable: Follow the communication cable between units. Look for staples through the jacket, rodent damage, or splices. Replace damaged sections with the same gauge and type of cable.
Tighten terminals: Loosen and re-tighten all communication terminal screws to ensure good contact. Oxidation or loose screws can cause intermittent E6 errors.
Power cycle: Restore power and leave the system off at the thermostat for 5 minutes, then call for cooling. Many Trane controls will reinitialize communication during this period.

If E6 persists, a technician should check for firmware issues and may need to replace the indoor or outdoor control board.

Trane air conditioner shows E6 and may not respond to thermostat commands; indoor and outdoor units may not coordinate.

Possible Causes