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Error code reference

Bosch Refrigerator Error Code FD

FD-sensor (freezer defrost sensor) disconnection or short circuit.

Bosch codesBosch refrigerator codes

FD-sensor (freezer defrost sensor) disconnection or short circuit.

First step from the service manual

Measure the resistance between both terminals after separating CN15 of the Main PCB. If FD-sensor is disconnected or shorted, change the FD-sensor on the evaporator.

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

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What FD means on a Bosch refrigerator

The FD error code on a Bosch refrigerator indicates a fault detected in the FD-sensor, which is the freezer defrost sensor. This sensor is mounted on the evaporator coil inside the freezer compartment and is responsible for monitoring temperature during the defrost cycle. The main PCB uses readings from this sensor to determine when the evaporator has reached the correct temperature to terminate a defrost cycle. When the control board detects either an open circuit (disconnection) or a short circuit condition in the sensor circuit, it logs the FD fault and may suspend normal defrost operation.

The diagnostic process begins at connector CN15 on the main PCB. After unplugging this connector, a resistance measurement is taken across both sensor terminals. A disconnected sensor will show an open circuit with infinite resistance, while a shorted sensor will read near zero ohms. Either condition falls outside the normal operating resistance range for a functioning thermistor-type defrost sensor, confirming the fault. The measurement must be taken directly at the sensor leads after separating the connector from the board to rule out wiring harness issues between the sensor and the PCB.

Common causes include physical damage to the sensor from ice buildup, corrosion at the connector terminals, a faulty sensor thermistor, or wiring that has chafed or broken near the evaporator. If the wiring and connector check out but the resistance reading is still out of range, the FD-sensor itself on the evaporator must be replaced to clear the fault.

Source: manufacturer service documentation.

Common causes of FD

  1. 01

    Failed FD-sensor thermistor

    Part replacement

    The thermistor element inside the sensor degrades over time and can develop an open or short circuit internally. This is confirmed when resistance measured directly at the sensor terminals is either infinite or near zero ohms.

  2. 02

    Disconnected sensor wiring

    Wiring / connection

    The sensor connector or wiring harness between the FD-sensor and CN15 on the main PCB can become loose or disconnected, particularly due to frost accumulation or physical movement during servicing. This produces an open circuit reading.

  3. 03

    Corroded or damaged connector terminals

    Wiring / connection

    Moisture inside the freezer compartment can corrode the terminals at the CN15 connector or at the sensor connector itself, causing intermittent or permanent loss of continuity. Inspect terminals closely for oxidation or pitting.

  4. 04

    Chafed or broken sensor wire

    Part replacement

    Wiring running from the evaporator sensor to the main PCB can crack or break from repeated freeze-thaw cycles or contact with sharp metal edges inside the cabinet. A visual inspection of the full wire run can identify this.

  5. 05

    Ice damage to sensor body

    Part replacement

    Excessive ice buildup on the evaporator can physically stress or crack the sensor housing, damaging the internal sensing element. This is more likely if previous defrost cycles were incomplete.

See the test procedure for each cause

Frequently asked questions about FD

What does FD mean on a Bosch refrigerator?
The FD code on a Bosch refrigerator indicates that the freezer defrost sensor, known as the FD-sensor, has either become disconnected or has developed a short circuit. This sensor is located on the evaporator coil in the freezer and monitors temperature during the defrost cycle. The main PCB detects the fault by identifying an abnormal resistance reading in the sensor circuit and triggers the FD error code in response.
Can I fix the FD error code on my Bosch refrigerator myself?
A knowledgeable DIYer with a multimeter can perform the initial diagnostic by separating connector CN15 from the main PCB and measuring resistance across the FD-sensor terminals. If the reading confirms an open or short circuit, the FD-sensor on the evaporator must be replaced. Accessing the evaporator typically requires removing freezer shelving and panels, so comfort with appliance disassembly is necessary. If the wiring or connector appears damaged rather than the sensor itself, a repair may be possible without ordering parts.
Is it safe to keep using my Bosch refrigerator with the FD error code showing?
Continued use with an FD error is not recommended for the long term, because the defrost cycle may not operate correctly without a functioning FD-sensor. This can lead to frost buildup on the evaporator coil, reduced cooling efficiency, and potential food spoilage. It is best to address the fault promptly to prevent secondary damage to other refrigerator components.
How much does it cost to repair the FD error on a Bosch refrigerator?
Repair costs vary depending on whether only the sensor needs replacement or if additional wiring or board work is required. The FD-sensor part itself is generally a low-cost component, typically in the range of $15 to $50. If a technician is hired for diagnosis and replacement, total service costs including labor commonly fall in the range of $100 to $250 depending on your location and service provider.
Will resetting my Bosch refrigerator clear the FD error code?
A power reset may temporarily clear the FD code from the display, but the error will return if the underlying sensor fault has not been corrected. The main PCB continuously monitors the FD-sensor circuit during operation, so any ongoing disconnection or short circuit will retrigger the fault. A permanent resolution requires confirming the sensor resistance is within normal range, which means repairing or replacing the faulty sensor or wiring.

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