42
Bryant Inducer or Blower Communication Fault (ECM/Variable-Speed Models)

Furnace LED shows code 42; unit may short-cycle or fail to respond correctly to thermostat calls.

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Failed ECM motor module, communication wiring fault between motor and control board, defective control board

How to Fix / Troubleshooting

Safety first: Turn off power before disconnecting any motor or control wiring.

  • Inspect communication harness: On variable-speed Bryant furnaces, check the low-voltage communication cable between the ECM motor and the furnace control board. Ensure connectors are fully seated and wires are not pinched.
  • Check for water damage: Look for signs of condensate leakage onto the motor or control board. Correct any drain issues before replacing electronics.
  • Power reset: Turn off power for 5 minutes, then restore. Sometimes an ECM motor can recover from a transient fault.

Because code 42 involves communication electronics, accurate diagnosis usually requires manufacturer-specific tools. If the code returns, have a technician test the ECM motor and control board.

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Repair Difficulty

Professional Required 5/5

Required Part

ECM Blower Motor Module
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