Thermostat displays E3 and system shuts down heating or cooling

Safety first: Turn off power to both the indoor air handler/furnace and the outdoor condenser/heat pump at their disconnects and breakers.

Steps to resolve E3 outdoor sensor error:

• 1. Locate outdoor sensor: Find the Goodman outdoor temperature sensor mounted near the outdoor unit or on the north-facing exterior wall. Follow the low-voltage cable back to the unit or thermostat.
• 2. Inspect physical condition: Check the sensor for cracks, UV damage, or impact damage. Ensure the sensor is not submerged in water or buried in debris.
• 3. Check wiring: Inspect the low-voltage cable for cuts, rodent damage, or pinch points. Verify tight connections at the thermostat OT terminals and at any junctions near the outdoor unit.
• 4. Measure resistance: With power off, disconnect the sensor leads at the thermostat and measure resistance across them. Compare to Goodman outdoor sensor resistance charts for the current outdoor temperature. Out-of-range readings indicate a bad sensor.
• 5. Temporarily disable sensor: If the thermostat allows, disable the outdoor sensor feature in the installer menu. If E3 clears and the system operates normally, the sensor or wiring is the cause.
• 6. Replace sensor: Install a new Goodman-compatible outdoor temperature sensor, using UV-rated low-voltage cable if the existing cable is damaged. Seal all exterior penetrations with appropriate sealant.