Error code reference

Bosch Dishwasher Error Code #B

Apexx display

Bosch codesBosch dishwasher codes

Apexx display: Aqua Sensor (green) fault.

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What #B means on a Bosch dishwasher

Error code #B on a Bosch dishwasher with an Apexx display signals a fault in the Aqua Sensor circuit, specifically the green-channel reading. The Aqua Sensor is an optical turbidity and clarity sensor that monitors wash water quality in real time, allowing the control board to adjust cycle parameters based on how dirty or clear the water is. When the control board detects an out-of-range or implausible signal from the Aqua Sensor's green light emitter or receiver, it logs code #B and may interrupt or alter the wash cycle.

For homeowners, the Aqua Sensor is a small optical device typically mounted in the sump area at the bottom of the dishwasher tub. It shines a light through the wash water and measures how much passes through. If the sensor is coated with grease, limescale, or detergent residue, it can send a faulty reading to the control board even if the sensor itself is physically intact. This means the fix is sometimes as simple as cleaning the sensor lens. In other cases, the sensor itself has failed electrically or the wiring connecting it has corroded or come loose, requiring part replacement. Running the dishwasher with this fault active may result in poor wash performance because the machine cannot accurately calibrate the cycle to actual water conditions.

Source: manufacturer service documentation.

Common causes of #B

  1. 01

    Contaminated or fouled Aqua Sensor lens

    Wiring / connection

    Grease, limescale, or detergent film built up on the optical lens of the Aqua Sensor blocks or distorts the green-channel light beam, causing the control board to read the signal as out of range. Cleaning the sensor surface often resolves this without any parts.

  2. 02

    Failed Aqua Sensor (green channel)

    Part replacement

    The green light emitter or receiver inside the Aqua Sensor has degraded or failed electrically, producing a signal the control board cannot interpret as valid. A failed sensor must be replaced to clear the fault.

  3. 03

    Damaged or disconnected wiring harness to the Aqua Sensor

    Part replacement

    The connector or wire leads running from the Aqua Sensor to the control board may be corroded, pinched, or have worked loose over time, interrupting the signal. Inspecting and reseating or repairing the harness is required, and a badly corroded harness will need replacement.

  4. 04

    Faulty control board failing to read the Aqua Sensor signal

    Part replacement

    If the sensor and wiring test within spec but the fault persists, the control board's input circuit for the Aqua Sensor may have failed, preventing it from correctly interpreting even a good signal. This is the least common cause and should only be suspected after the sensor and harness are confirmed good.

See the test procedure for each cause

Frequently asked questions about #B

What does error code #B mean on a Bosch dishwasher?
Error code #B on a Bosch dishwasher with an Apexx display indicates a fault with the Aqua Sensor, specifically its green optical channel. The Aqua Sensor monitors wash water clarity and turbidity so the control board can adjust cycle settings automatically. When the sensor sends a signal outside expected parameters, the board registers code #B. The cause can be a dirty sensor lens, a failed sensor, or a wiring problem.
How do I fix error code #B on my Bosch dishwasher?
Start by locating the Aqua Sensor in the sump area at the bottom of the tub and cleaning its optical lens with a soft cloth and a mild descaling solution to remove grease or limescale buildup. If cleaning does not clear the code after running a cycle, check that the wiring harness connector to the sensor is fully seated and free of corrosion. If the fault persists, the Aqua Sensor itself likely needs to be replaced. Sensor replacement is a moderate DIY repair requiring sump access; if you are not comfortable working around dishwasher electrical components, a qualified appliance technician can complete it.
Can I still use my Bosch dishwasher with error code #B active?
The dishwasher may still run cycles with code #B active, but wash performance will likely be degraded because the control board cannot use Aqua Sensor data to calibrate the cycle to actual water conditions. The machine may use default or fixed cycle parameters instead, which can result in dishes not being cleaned properly or excessive water and energy use. There is no immediate safety hazard from this fault, but continued use without resolving the sensor issue is not recommended for consistent results.
How much does it cost to repair error code #B on a Bosch dishwasher?
If the Aqua Sensor only needs cleaning, the cost is essentially zero beyond your time. A replacement Aqua Sensor for a Bosch dishwasher typically costs between $20 and $60 for the part, depending on the specific model. If you hire a technician, expect to add $80 to $150 in labor, bringing the total repair to roughly $100 to $200. A wiring harness repair or control board replacement would push costs higher, so confirming the sensor is the actual failed component before ordering parts is worthwhile.
Where is the Aqua Sensor located in a Bosch dishwasher?
The Aqua Sensor is mounted in or near the sump assembly at the bottom of the dishwasher tub, typically along the base where wash water circulates. Accessing it usually requires removing the lower spray arm and the sump cover or filter assembly. The sensor is a small plastic component with a wiring harness connector and a clear or translucent optical window that must be kept clean to function correctly.

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