Bosch Dishwasher Error Code F91

F91 means the load size registration system is inactive on your Bosch dishwasher. Instead of adjusting the water intake based on how full the dishwasher is, the machine has defaulted to using a fixed water quantity for every cycle. This is typically caused by a problem with the speed sensor, which provides the data needed for load-dependent water management. The dishwasher will continue to operate, but at reduced efficiency.

A reset may temporarily clear the F91 code, but it will return if the underlying cause has not been repaired. Because F91 is triggered by a functional fault in the speed sensor or its circuit, the error will reappear as soon as the dishwasher attempts to run a cycle and detects the same problem again. Clearing the code without fixing the sensor or wiring is only a short-term measure.

Repair costs vary depending on the root cause. If only the speed sensor needs replacement, parts typically range from around $20 to $80, with professional labor adding $75 to $150 or more depending on your location. If the control board is found to be at fault, parts alone can range from $100 to $300 or higher, making professional diagnosis worthwhile before committing to that repair.

A knowledgeable DIYer can start by inspecting the speed sensor and its wiring harness for visible damage, corrosion, or loose connectors, which does not require purchasing parts. If the wiring appears intact, the speed sensor itself may need to be tested and replaced. Control board issues, if that is the root cause, are more complex and may benefit from professional diagnosis.

F91 is a performance fault rather than a safety-critical error, so the dishwasher is generally safe to use while it is active. However, the machine will not optimize water usage, meaning it may use more or less water than ideal for a given load. Running the dishwasher in this condition for an extended period without repair is not recommended, as it reduces efficiency and leaves the underlying sensor issue unresolved.