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Error code reference

Denso Air Conditioner Error Code FT

Freeze protection thermistor defect

Denso codesDenso air conditioner codes

Freeze protection thermistor defect — short or open circuit detected on freeze protection thermistor connected to J102.

First step from the service manual

Disconnect and reconnect the freeze protection thermistor. If it doesn't work, replace it.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What FT means on a Denso air conditioner

The FT error code on a Denso air conditioner indicates a defect detected on the freeze protection thermistor circuit. Specifically, the control board has identified either a short circuit or an open circuit condition on the thermistor wired to connector J102. The freeze protection thermistor monitors evaporator coil temperature to prevent ice buildup. When the resistance reading from this sensor falls outside the expected range, whether due to a short pulling resistance too low or an open circuit driving it to infinity, the system triggers the FT fault and disables operation to protect the equipment.

The freeze protection thermistor is a negative temperature coefficient (NTC) type sensor, meaning its electrical resistance decreases as temperature rises. A properly functioning thermistor produces a predictable resistance value at any given coil temperature. An open circuit, which can result from a broken wire, corroded terminal, or failed sensor element, will present infinite resistance to the control board. A short circuit, caused by damaged wiring insulation, moisture intrusion, or internal sensor failure, will present near-zero resistance. Either condition is outside acceptable operating parameters and triggers the FT code.

The most straightforward first step is to disconnect and reconnect the freeze protection thermistor at the J102 connector to rule out a loose or intermittent connection. Corrosion or a poorly seated connector pin can mimic a sensor failure. If reseating the connector does not resolve the fault, the thermistor itself requires replacement. Wiring continuity between the sensor and J102 should also be inspected for damage before condemning the thermistor.

Source: manufacturer service documentation.

Common causes of FT

  1. 01

    Loose or corroded connector at J102

    Wiring / connection

    A poorly seated or oxidized connector at the J102 terminal can interrupt the signal from the thermistor, mimicking an open circuit. Disconnecting and firmly reseating the connector often resolves this without part replacement.

  2. 02

    Failed freeze protection thermistor

    Part replacement

    The thermistor sensor element itself may have failed internally, producing either no resistance (short) or infinite resistance (open). A failed thermistor will not recover after reconnecting and requires replacement.

  3. 03

    Damaged wiring between thermistor and J102

    Part replacement

    The wiring harness connecting the freeze protection thermistor to the J102 connector can develop breaks or shorts due to chafing, pinching, or rodent damage. Inspect the full wire run for visible damage and test continuity.

  4. 04

    Moisture or contamination in the connector

    Wiring / connection

    Water intrusion into the J102 connector can cause corrosion on the terminals or create a short circuit between pins. Inspect the connector housing and terminals for moisture, rust, or oxidation.

  5. 05

    Control board fault misreading the thermistor circuit

    Part replacement

    In rare cases, the control board circuitry responsible for reading the J102 thermistor input can fail, causing a false FT code even when the sensor and wiring are intact. This should only be suspected after the thermistor and wiring have been confirmed good.

See the test procedure for each cause

Frequently asked questions about FT

What does FT mean on a Denso air conditioner?
The FT code indicates a defect detected on the freeze protection thermistor circuit connected to connector J102. The system has found either a short circuit or an open circuit on this sensor. The freeze protection thermistor monitors evaporator coil temperature to prevent ice formation, and the unit will not operate normally until the fault is corrected.
How do I fix the FT error code on a Denso air conditioner?
Start by disconnecting and firmly reconnecting the freeze protection thermistor at the J102 connector, as a loose or corroded connection is the most common cause. If the error returns, inspect the wiring harness between the thermistor and J102 for damage. If the wiring is intact and the connector is secure, the thermistor itself will need to be replaced.
Is it safe to run my Denso air conditioner with the FT error code active?
Operating the unit with an FT fault is not recommended. The freeze protection thermistor is a safety component that prevents the evaporator coil from icing over. Without a functioning sensor, the system cannot detect coil freeze conditions, which can lead to reduced airflow, compressor damage, or refrigerant issues over time.
Will resetting the unit clear the FT error code?
A power reset may temporarily clear the FT code, but the fault will return if the underlying problem with the thermistor or its wiring has not been corrected. The recommended first step is to disconnect and reconnect the thermistor before cycling power, as this addresses the most common cause. A persistent fault after reconnection and reset indicates the thermistor needs replacement.
How much does it cost to repair a Denso FT error code?
If the issue is simply a loose connector, there may be no parts cost involved, only a service call fee which typically ranges from $75 to $150 depending on your location. If the freeze protection thermistor needs replacement, parts and labor combined generally range from $100 to $300. Wiring harness repairs or control board replacement would fall on the higher end of that range or beyond.

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