Thermostat displays E2 and system will not respond to heating or cooling commands.

Safety first: Shut off power to the outdoor condensing unit/heat pump and indoor unit at the service disconnect and breaker panel.

Steps to troubleshoot:

• 1. Reset power: Turn off both indoor and outdoor breakers for 2–3 minutes, then restore power. Check if E2 clears after reboot.
• 2. Inspect ABCD wiring at outdoor unit: Remove the service panel on the Bryant outdoor unit. Locate the ABCD low-voltage terminals on the control board. Verify each conductor is tight and matches the color and position used at the indoor unit (A to A, B to B, etc.).
• 3. Check for corrosion or water intrusion: Look for rusted terminals, water in the control compartment, or green/white corrosion on wires. Clean light corrosion and re-terminate wires; replace severely corroded connectors.
• 4. Inspect cable run: Trace the low-voltage cable between indoor and outdoor units. Look for cuts, crushed sections, or splices exposed to weather. Replace damaged cable with outdoor-rated thermostat wire.
• 5. Test with temporary cable: If possible, run a temporary 4-conductor cable from indoor unit to outdoor unit. If E2 clears, the original cable is defective.
• 6. Professional service: If wiring is confirmed good and E2 persists, the outdoor control board or indoor control board may have a failed communication circuit and should be tested and replaced by a Bryant technician.