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Error code reference

Gaggenau Oven Error Code E123

Core temperature sensor too low (<-10°C / 50°F, resistance ≈ 200 kohm)

Gaggenau codesGaggenau oven codes

Core temperature sensor too low (<-10°C / 50°F, resistance ≈ 200 kohm) – sensor break cooking compartment 1 (up to software 1.20 not displayed).

First step from the service manual

Check temperature sensor with service test programme. Check resistance value (25°C/77°F ≈ 50 kohm, 70°C/158°F ≈ 8.77 kohm). Replace KTF temperature sensor.

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

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What E123 means on a Gaggenau oven

Error code E123 on a Gaggenau oven indicates that the core temperature sensor (KTF) for cooking compartment 1 is reading below -10°C (50°F), which corresponds to a resistance of approximately 200 kohm or higher. This value falls well outside the expected operating range for the NTC-type temperature sensor used in this system, and the oven interprets the abnormal resistance as a sensor break condition. It is worth noting that on units running software version 1.20 or earlier, this fault code will not be displayed on the control panel, meaning the failure may be silent on older firmware.

The core temperature sensor (KTF) is the probe responsible for monitoring internal food or compartment temperature during cooking. Its resistance changes predictably with temperature: at 25°C (77°F) the sensor should measure approximately 50 kohm, and at 70°C (158°F) the resistance should drop to approximately 8.77 kohm. A reading near 200 kohm suggests the circuit is either open due to a broken sensor element, a disconnected or corroded connector, or damaged wiring in the sensor circuit.

Diagnosis should begin with the service test programme to confirm the fault, followed by a direct resistance measurement of the KTF sensor at known ambient temperature. If the measured resistance does not align with the expected values listed above, the sensor itself is the most likely failure point. Wiring continuity and connector integrity between the sensor and the control board should also be inspected before condemning the sensor, as loose or corroded terminals can produce the same open-circuit resistance reading.

Source: manufacturer service documentation.

Common causes of E123

  1. 01

    Failed KTF temperature sensor

    Part replacement

    The NTC sensor element itself can break internally, causing resistance to spike well above the expected range. Measuring the sensor at room temperature and comparing against the 25°C specification of approximately 50 kohm will confirm this failure.

  2. 02

    Disconnected or loose sensor connector

    Wiring / connection

    A connector that has vibrated loose or was not fully seated will create an open circuit that reads the same as a broken sensor. Inspect all connectors in the KTF sensor wiring path and reseat any that appear loose.

  3. 03

    Damaged sensor wiring

    Part replacement

    Wiring routed near heating elements can become brittle, cracked, or burnt over time, interrupting continuity in the sensor circuit. A visual inspection and continuity check of the sensor leads will identify this issue.

  4. 04

    Corroded connector terminals

    Wiring / connection

    Moisture or grease contamination inside the sensor connector can cause high resistance at the contact points, mimicking an open circuit. Cleaning or replacing the affected terminals may restore normal sensor readings.

See the test procedure for each cause

Frequently asked questions about E123

What does E123 mean on a Gaggenau oven?
E123 means the core temperature sensor (KTF) for cooking compartment 1 is reading below -10°C (50°F), which corresponds to a resistance of approximately 200 kohm. This value indicates a sensor break condition, meaning the sensor circuit is open due to a failed sensor, broken wire, or loose connection. On ovens running software version 1.20 or earlier, this code will not appear on the display even though the fault is present.
Can I fix E123 myself or do I need a technician?
A knowledgeable DIYer can perform basic checks such as inspecting connectors and measuring sensor resistance with a multimeter. The expected resistance values are approximately 50 kohm at 25°C (77°F) and 8.77 kohm at 70°C (158°F), making it straightforward to verify whether the sensor is faulty. However, accessing the sensor wiring and running the service test programme may require disassembly and technical familiarity with the appliance, so professional service is recommended if you are not comfortable with those steps.
Is it safe to use my Gaggenau oven while E123 is active?
Operating the oven with a broken core temperature sensor means the appliance cannot accurately monitor compartment temperatures, which could lead to undercooked food or uncontrolled heating cycles. It is best to avoid using the oven for cooking until the sensor fault has been diagnosed and repaired. If the oven is not entering a cook cycle at all due to the error, do not attempt to bypass the fault.
Will resetting the oven clear the E123 error code?
A power reset may temporarily clear the displayed error, but E123 will return as soon as the control board reads the sensor resistance again and detects the out-of-range value. The underlying cause, whether a broken sensor, open wire, or loose connector, must be physically corrected to permanently resolve the fault.
How much does it cost to repair a Gaggenau oven showing E123?
If the KTF temperature sensor itself needs replacement, parts and labor costs can range from around $150 to $400 or more depending on your region and service provider. If the issue turns out to be a loose connector or damaged wire rather than a failed sensor, repair costs may be lower since no replacement part is needed. Gaggenau is a premium appliance brand, so professional diagnostic fees alone can range from $80 to $150 before any parts are ordered.

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