Indoor unit shows CH03 and may not respond to remote commands or may shut down unexpectedly.

Safety: Turn off the outdoor unit's disconnect or breaker. Do not work inside the outdoor unit with power on.

Steps:

• Power cycle: Turn OFF power for 5–10 minutes, then ON. If CH03 returns, continue.
• Open outdoor unit: Remove the service panel to access the control board and coil area.
• Locate outdoor pipe thermistor: It is clipped to the outdoor heat exchanger tubing, with two wires leading back to the PCB.
• Check physical condition: Ensure the sensor is firmly attached to the coil tube and not corroded or broken. Reclip if loose.
• Inspect wiring and connector: Look for rodent damage, UV-brittled insulation, or loose plugs. Reseat the connector on the outdoor PCB.
• Test resistance: With power OFF, measure resistance across the thermistor. An infinite or near-zero reading indicates a bad sensor.
• Replace sensor: If faulty, install a new LG outdoor pipe thermistor. Use the original mounting clip and route wires away from fan blades and hot discharge lines.
• Reassemble and test: Refit the panel, restore power, and run the system in COOL or HEAT to verify CH03 is cleared.

Technician recommended: If the sensor and wiring are intact but CH03 persists, the outdoor PCB may need replacement and should be evaluated by a licensed technician.