Fujitsu ASTG09 / ASTG12 / AOTG09 / AOTG12 KMTC error code 41
Room temperature sensor error
Quick answer
On Fujitsu ASTG09 / ASTG12 / AOTG09 / AOTG12 KMTC, 41 is a fault. It means room temperature sensor error. A first thing to check: A failed room temperature thermistor.
- Applies to
- Fujitsu ASTG09 / ASTG12 / AOTG09 / AOTG12 KMTC
- Fujitsu GENERAL AIRSTAGE KMTC wall split codes, indoor and outdoor · Mini Split
- Type of code
- Fault
- Urgency: Book a technician
- First safe check
- Measure the room thermistor resistance and compare it to 33.6 kOhm at 0 C, 12.5 kOhm at 20 C and 8.0 kOhm at 30 C.
What 41 means on this model
The thermistor that reads the room air has failed, so the unit has stopped because it cannot know what temperature the room is at. The thermistor is the room sensor designated ThR, and the documented test is a resistance check against the table: it should read 33.6 kOhm at 0 C, 12.5 kOhm at 20 C, and 8.0 kOhm at 30 C. Those three numbers are the fastest way to tell a failed sensor from a wiring fault, because a sensor that is open reads infinite and a shorted one reads near zero rather than sitting somewhere off the curve.
Symptoms you will notice
- Code 41 and the unit will not hold the room at setpoint
- The system runs but the room temperature control is wrong
- The controller shows a room temperature that does not match a thermometer
- The fault appeared after a service on the indoor unit
Common causes
The code tells you what the control detected, not which part failed. These are the causes we see most often, roughly in order of likelihood:
- A failed room temperature thermistor
- A short or open in the wiring to the sensor
- A connector that has been disturbed
- A sensor that has been moved away from the air stream it is meant to read
What you can safely check
These are homeowner-level checks. None of them need you to open a live electrical compartment or work on gas.
- Measure the room thermistor resistance and compare it to 33.6 kOhm at 0 C, 12.5 kOhm at 20 C and 8.0 kOhm at 30 C.
- Check the connector and the wire at the sensor.
- Check that the sensor is still positioned where it reads room air and has not been moved during a filter or coil service.
Do not do these
- ×Do not replace the sensor because the room feels warm. A failed sensor stops the unit, and an unmeasured room temperature is the reason, not a comfort setting.
- ×Do not work on the sensor connector with the power switch on.
When to call a technician
Worth scheduling, and worth your own checks first
You can usually keep living with this for a short while, but it will not fix itself. Do the safe checks below first, because a tripped switch or a blocked airflow is a five-minute fix that would otherwise cost you a service call.
- The refrigerant circuit is sealed and legally requires licensed handling. Opening it without certification releases refrigerant and can put the whole system in violation of regulation, so a low-pressure or high-pressure fault on this equipment is a call-out, not a weekend job.
- If the appliance has stopped mid-cycle, is making a noise you have not heard before, or smells burnt, stop reading here and call. Those are symptoms of something the fault code does not describe well enough.
A technician job once the sensor is involved.
What it costs to fix
Parts
Room temperature thermistor $25 to $80.
Labor
One to two hours to test and replace.
DIY or technician
A technician job once the sensor is involved.
Typical US part and labor ranges, 2026. They vary by region, model and contractor, so treat them as a planning figure, not a quote.
Scope of this code
- Code table
- Fujitsu GENERAL AIRSTAGE KMTC wall split codes, indoor and outdoor
- Models in scope
- Fujitsu ASTG09 / ASTG12 / AOTG09 / AOTG12 KMTC
- Checked
- Confirm on your own unit
- Find the model number on the data plate, then check this code in the service manual for that model. Manufacturers revise code tables between model years, and a revised board can renumber a fault.