u3
Moderate
Mitsubishi Electric · Mini-Splits & Ductless Systems
Open / Short Circuit Sensor Detection
Quick Answer
Error code U3 on your Mitsubishi Electric Mini-Splits & Ductless Systems means: Open / Short Circuit Sensor Detection. This is usually fixable — see the step-by-step guide below.
Likely Causes
How to Fix It
1
Identify which sensor is faulted by checking each outdoor sensor's resistance with a multimeter
2
Compare each reading to the Mitsubishi temperature-resistance chart for the current conditions
3
Inspect all outdoor sensor connectors at the PCB for corrosion and clean if needed
4
Check sensor wiring for physical damage along the routing path
5
Replace any sensor found to be open or shorted
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Outdoor temperature sensors (as identified)
Wire connectors
Sensor mounting hardware
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