E03 displayed and thermostat cannot read remote indoor sensor; remote room temperature not available.

Safety: Turn off power to the HVAC system at the breaker before working on thermostat wiring.

• Step 1 – Verify sensor configuration: In the thermostat installer menu, confirm that a remote indoor sensor is actually enabled. If no sensor is installed, disable the feature to clear E03.
• Step 2 – Inspect wiring at thermostat: Remove the thermostat from the wall plate. Check the remote sensor terminals (often labeled S1/S2 or similar). Ensure wires are firmly clamped and not shorted together.
• Step 3 – Inspect sensor at remote location: Remove the remote sensor cover. Check for loose connections, corrosion, or damage. Tighten terminal screws and ensure no bare wires are touching.
• Step 4 – Test sensor resistance: With power off and wires disconnected at both ends, measure resistance across the sensor leads with a multimeter. Compare to Johnson Controls’ NTC sensor chart (e.g., ~10kΩ at 77°F/25°C). Infinite or near‑zero resistance indicates a failed sensor or wiring.
• Step 5 – Repair or replace: Repair any damaged cable runs (splices in a junction box) or replace the Johnson Controls remote room temperature sensor if readings are out of spec.