Trane air conditioner displays E9 and may not maintain set temperature; system may short-cycle.

Safety first: Turn off power to the indoor unit before accessing the control compartment.

• Locate sensor: On ducted Trane air handlers, the indoor temperature sensor (thermistor) is typically mounted near the return air or on the evaporator coil. On ductless systems, it is behind the front grille.
• Check connection: Ensure the thermistor plug is fully seated on the control board and that wires are not pinched or broken.
• Inspect sensor: Look for corrosion, physical damage, or if the sensor has come loose from its mounting clip. Re-secure it in the airstream if displaced.
• Reset system: Restore power and clear the error by turning the thermostat off for a few minutes, then back on.

If E9 persists, the thermistor likely needs replacement with a Trane-approved sensor matched to the control board.