Trane air conditioner control board display shows E0 and system will not start cooling or heating.

Safety first: Turn off power to both indoor air handler/furnace and outdoor Trane condenser at the breaker and service disconnect before touching any wiring.

• Verify thermostat operation: Confirm the thermostat is powered and set to COOL with a temperature below room temperature. Replace thermostat batteries if applicable.
• Inspect low-voltage wiring: Remove the access panel on the outdoor unit and indoor air handler. Check the low-voltage (typically 18 AWG red/white/yellow/green/common) wires between the thermostat, indoor control board, and outdoor contactor/control board. Look for loose wire nuts, broken conductors, corrosion, or rodent damage. Tighten any loose connections and repair damaged sections with proper wire splices and electrical tape.
• Check communication terminals: On many Trane systems, the Y, C, R, and sometimes dedicated communication terminals must be correctly landed. Compare wiring to the unit’s wiring diagram on the service panel. Correct any miswired connections.
• Reset power: After correcting wiring, restore power at the breaker and disconnect. Wait 5–10 minutes for the Trane control board to reboot and re-establish communication. See if the E0 code clears and the system starts.
• Board inspection: If wiring is intact, visually inspect the indoor and outdoor control boards for burnt components, swollen capacitors, or water damage. If damage is visible, the board likely needs replacement by a qualified technician.

If the E0 code persists after wiring verification and power reset, contact a Trane-certified technician to test low-voltage circuits and replace the appropriate control board.