Bosch · Dishwasher

E9

AquaSensor Malfunction

Severity

Low

Seeing E9 on your Bosch Dishwasher display means the appliance self-diagnostic detected "AquaSensor Malfunction". Before calling a technician, work through the steps in this guide — the fix is often simpler than you think.

Owner's Summary

The AquaSensor is an optical sensor that measures water cloudiness to optimize the wash cycle. When it gets cloudy from limescale or food residue, it gives incorrect readings. Running a descaling cycle often resolves E9 completely.

Symptoms

Bosch dishwasher displaying E9, not completing eco cycle correctly

Common Causes

Dirty or calcified AquaSensor optical lens
Wiring fault to AquaSensor
Defective AquaSensor unit
PCB communication failure with sensor

How to Fix

1 Clean the AquaSensor lens located in the sump area with a soft cloth
2 Run a cleaning cycle with dishwasher descaler
3 Inspect wiring connector to AquaSensor
4 Replace AquaSensor if cleaning does not resolve the issue

Tools You'll Need

Vinegar or Descaler Electrical Contact Cleaner Flashlight

These are simple, low-risk fixes most homeowners can do with tools already in a basic toolbox.

Technical Explanation

The Bosch AquaSensor uses an infrared LED and photodetector to measure water turbidity. The EGO module reads the sensor output voltage continuously. E9 is generated when the sensor output is outside the valid operating window, indicating contamination or failure of the optical components.

Is It Safe to Keep Using?

Low risk. The machine may default to a full program without sensor optimization. Fix within a few weeks.

Technician's Pro Tip

E9 is very common in hard water areas. A 30-minute soak with citric acid or commercial descaler placed in the bottom of the tub, followed by a hot rinse cycle, resolves the majority of E9 errors without replacing any parts.

Related Codes

E1 — Bosch Washing Machine

Water Intake Fault

High

E18 — Bosch Washing Machine

Drain Fault — Water Not Pumping Out

High

E17 — Bosch Washing Machine

Water Intake Too Slow

Medium

Frequently Asked Questions

What does error code E9 mean on a Bosch Dishwasher?

Code E9 on a Bosch Dishwasher indicates "AquaSensor Malfunction." In practice, the most common trigger is dirty or calcified AquaSensor optical lens. Severity is rated low, and typical repair costs range from $5 to $150.

Can I fix E9 myself, or do I need a technician?

Many cases of E9 can be resolved without a technician. The first step to try: clean the AquaSensor lens located in the sump area with a soft cloth. If that doesn't clear the code, work through the remaining steps in the "How to Fix" section above before assuming a part needs replacing.

Is it safe to keep using my dishwasher with code E9 showing?

Low risk. The machine may default to a full program without sensor optimization. Fix within a few weeks.

How much does it cost to repair E9 on a Bosch Dishwasher?

Repair costs for code E9 typically range from $5 to $150. Descaler cleaning: $5–$15; AquaSensor replacement: $40–$150. Costs on the low end usually reflect a DIY fix with no parts required, while the high end reflects a part replacement plus professional labor.

Estimated Repair Cost USD

$5 – $150

Descaler cleaning: $5–$15; AquaSensor replacement: $40–$150