Bosch Dishwasher Error Code #B

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.

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.

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.

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.

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.