Error code reference

Bosch Dishwasher Error Code #A

Apexx display

Bosch codesBosch dishwasher codes

Apexx display: Aqua Sensor (red) fault.

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What #A means on a Bosch dishwasher

The #A error code on a Bosch dishwasher with an Apexx display indicates a fault with the Aqua Sensor, flagged in red by the control board. The Aqua Sensor monitors water turbidity and clarity during the wash cycle, allowing the dishwasher to adjust water usage and cycle length based on how dirty the water is. When the control board receives a signal outside the expected range from this sensor, or receives no signal at all, it triggers the #A code and halts or interrupts normal operation.

For homeowners, the Aqua Sensor is a small optical sensor that essentially 'reads' how dirty your wash water is. When this sensor fails or sends bad data, the dishwasher cannot make accurate decisions about how long to wash or how much water to use, so it stops and alerts you with this code. The fault does not necessarily mean the sensor itself is broken; a contaminated sensor lens, a wiring problem, or a failed sensor module can all produce this error.

Because the Aqua Sensor is tied directly to wash cycle logic on Apexx-platform Bosch machines, this code should be addressed before continued regular use. Running cycles with a faulty Aqua Sensor can result in poor wash performance or erratic cycle behavior.

Source: manufacturer service documentation.

Common causes of #A

  1. 01

    Contaminated or fouled Aqua Sensor lens

    Wiring / connection

    Grease, detergent residue, or hard water deposits can coat the optical lens of the Aqua Sensor, causing it to misread water clarity and trigger a fault. Cleaning the sensor lens is the first physical check to perform before replacing any parts.

  2. 02

    Failed Aqua Sensor module

    Part replacement

    The sensor itself can fail internally, causing it to output a constant incorrect signal or no signal at all. A failed Aqua Sensor module will not respond to cleaning and must be replaced.

  3. 03

    Damaged or disconnected wiring harness to the Aqua Sensor

    Part replacement

    The wiring harness connecting the Aqua Sensor to the control board can develop an open circuit, short, or loose connector, preventing accurate signal transmission. Inspecting the harness for visible damage or a loose plug is a key diagnostic step.

  4. 04

    Faulty control board

    Part replacement

    If the wiring and Aqua Sensor both test correctly, the main control board may be misinterpreting or failing to read the sensor signal. Control board failure is the least common cause of this specific code but cannot be ruled out after other components are confirmed functional.

See the test procedure for each cause

Frequently asked questions about #A

What does error code #A mean on a Bosch dishwasher?
Error code #A on a Bosch dishwasher with an Apexx display means the control board has detected a fault with the Aqua Sensor, indicated in red. The Aqua Sensor monitors how dirty the wash water is during a cycle. The fault can be caused by a dirty sensor lens, a failed sensor, or a wiring issue between the sensor and the control board.
Can I still use my Bosch dishwasher with error code #A active?
It is not recommended to continue using the dishwasher normally with the #A code active. Because the Aqua Sensor controls how the wash cycle adjusts to water conditions, a fault can result in poor cleaning performance, incorrect water usage, or erratic cycle behavior. Address the sensor issue before running further cycles.
How do I fix error code #A on a Bosch dishwasher?
Start by locating the Aqua Sensor, which sits in the sump area of the dishwasher, and clean its optical lens with a soft cloth to remove any grease or mineral deposits. If the code returns after cleaning, check the wiring harness connected to the sensor for loose plugs or visible damage. If the harness is intact and the code persists, the Aqua Sensor module itself likely needs replacement. A repair technician can confirm sensor failure with a resistance or voltage reading.
How much does it cost to fix the #A error code on a Bosch dishwasher?
If the issue is a dirty sensor lens, the fix costs nothing beyond your time. A replacement Aqua Sensor module for a Bosch dishwasher typically costs between $20 and $60 for the part. If you hire a technician, expect to add $80 to $150 in labor depending on your area. A wiring harness repair or control board replacement would cost more and warrants a professional diagnosis first.
Is the Aqua Sensor on a Bosch Apexx dishwasher easy to replace?
Replacing the Aqua Sensor is a moderate DIY repair. The sensor is located in or near the sump area and typically requires removing the lower spray arm and filter assembly to access it. The sensor usually clips or screws into place and connects via a wire harness plug. A homeowner comfortable with basic appliance disassembly can complete this repair, but if you are uncertain about working near electrical connectors inside the tub area, a technician is a reasonable choice.

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