How to Fix Frigidaire Dishwasher Error Code tu: Turbidity sensor failure (Full Guide)

The “tu” error code on a Frigidaire dishwasher indicates a **Turbidity Sensor Failure**. This critical component, also known as an optical sensor, measures the “cloudiness” or clarity of the wash water to determine if more rinsing is needed. When the control board loses communication with this sensor or receives an irrational signal, it halts the cycle to prevent poor cleaning or mechanical damage.

While seeing an error code can be frustrating, the “tu” fault is rarely a death sentence for your appliance. Usually, it stems from a localized hardware issue—either a dirty lens, a loose wire, or a failed sensor diode. With a few basic tools and a bit of patience, you can diagnose and resolve this issue yourself, saving hundreds in professional repair fees. Your dishwasher isn’t broken; it’s just “blinded” and needs its eyes restored.

The Complete Solution

The Complete Solution: Step-by-Step Repair Guide

Follow these steps in order to diagnose and fix the “tu” error code.

1. Safety First: Power and Water Isolation

Before performing any work, disconnect the dishwasher from its power source. If it is plugged into a wall outlet under the sink, unplug it. If it is hardwired, flip the dedicated breaker in your home’s electrical panel. **Warning: Never work on a dishwasher with the power on; water and electricity are a lethal combination.** You do not necessarily need to turn off the water supply for this repair, but it is recommended if you plan on moving the unit significantly.

2. Gain Access to the Components

Open the dishwasher door and remove the bottom dish rack. Locate the kickplate (toe kick) at the very bottom of the unit near the floor. Use your screwdriver (usually a Phillips or Torx T20) to remove the two to four screws holding the kickplate in place. Once removed, set the plate aside. You will now see the motor, pump, and various sensors underneath the tub.

3. Locate and Inspect the Turbidity Sensor

The turbidity sensor is typically located on the bottom of the sump assembly (the large plastic housing that holds the water). It is a small plastic component with a wire harness plugged into it.

• Visual Check: Unplug the wire harness by pressing the locking tab. Inspect the pins for any green crust or black soot. If you see corrosion, clean the pins with a small brush and electronic contact cleaner.
• The “Wipe Test”: Sometimes, you can reach the sensor lens from *inside* the tub by removing the filters. Clean the plastic lens area with a microfiber cloth and white vinegar to remove any film.

4. Electrical Testing with a Multimeter

To confirm the sensor is dead, set your multimeter to the Ohms (Ω) setting. Place the probes on the terminals of the sensor (not the wires). While exact resistance values vary by model, a reading of “Open” (O.L) or “0” usually indicates a dead internal circuit. If the sensor also acts as a thermistor, you should see a resistance reading that changes if you apply heat (like from a hairdryer) to the sensor tip. If the reading stays static or shows no continuity, the part must be replaced.

5. Replacing the Sensor

If cleaning and reseating the wires didn’t work, you need to install a new part.

1. Place a towel under the sump area, as a small amount of residual water will leak out.
2. Most Frigidaire turbidity sensors are held in place by a simple “twist and lock” mechanism or a plastic retaining clip. Rotate the sensor counter-clockwise about a quarter turn and pull it straight out of the sump.
3. Lubricate the O-ring on the **new** sensor with a tiny drop of rinse aid or water (do not use grease or oil) to ensure a watertight seal.
4. Insert the new sensor and twist it clockwise until it clicks into place.
5. Reconnect the wiring harness, ensuring the locking tab “clicks.”

6. Testing and Reassembly

Replace the kickplate and restore power to the unit. To clear the error code, you may need to perform a “Hard Reset.” Hold the **Cancel** button for at least 5 seconds or until the display changes. Start a “Rinse Only” or “Express” cycle to verify that the “tu” code does not return and that the unit fills and drains correctly. Check for leaks around the new sensor during the first 10 minutes.

Technical Explanation of the Fault

To fix the “tu” error, one must understand that the turbidity sensor is essentially an optical eye. It sends an infrared beam through the water to a receiver. If the water is dirty, the beam is blocked; if clean, the beam passes through. Here is why this system fails:

1. **Protein and Grease Film Encapsulation:** Over time, a fine layer of fats, oils, and undissolved detergent can coat the plastic lens of the sensor. Even if the water is clean, the sensor “sees” a blockage because of the film on its own housing. This leads to an “out of range” signal that triggers the error.
2. **Internal Component Degradation (LED/Phototransistor):** Inside the sensor are delicate electronic components. Constant exposure to extreme temperature fluctuations—moving from cold tap water to 140°F (60°C) sterilized water—eventually causes the solder joints or the LED diode itself to fail. This is typical wear and tear after 5-7 years of service.
3. **Wiring Harness Corrosion:** Because the sensor is located at the bottom of the tub, it is susceptible to moisture. If the rubber O-ring seal develops a microscopic leak, water can enter the wiring harness connector. This causes “wicking” and corrosion (green oxidation) on the metal pins, breaking the electrical path to the main control board.
4. **Voltage Spikes or Logic Errors:** Occasionally, a surge in the home’s electrical system can scramble the calibration data stored on the dishwasher’s control board. While the sensor might be physically fine, the board no longer knows how to interpret its data, necessitating a hard reset or sensor replacement to re-establish a baseline.

Symptoms of a Frigidaire Turbidity Sensor Failure

When your Frigidaire dishwasher is struggling with a “tu” error, the symptoms go beyond just the code on the display. You may notice:

• The “tu” or “tU” Display: The most obvious sign is the digital display flashing these characters, often accompanied by a persistent beeping sound.
• Premature Cycle Shutdown: The dishwasher may start a cycle normally, drain the initial water, and then stop abruptly after five to ten minutes once it attempts to calibrate the water clarity.
• Lukewarm Water: On many Frigidaire models, the turbidity sensor is integrated with the thermistor (temperature sensor). If the “tu” error is active, the heating element may fail to engage, leaving your dishes wet and greasy.
• Extended Cycle Times: Before the sensor fails completely, you might notice cycles running for 3+ hours as the machine “hunts” for a clear water reading that never comes.
• Poor Cleaning Performance: Dishes may come out with a fine film of grit or food particles because the machine cannot accurately determine when the water is clean enough to stop rinsing.

How to Prevent Error “tu” from Returning

Once you have restored your dishwasher to working order, follow these maintenance protocols to ensure the sensor remains functional for years to come:

• Monthly Deep Clean: Run an empty cycle once a month using a dedicated dishwasher cleaner or a bowl of white vinegar placed on the top rack. This dissolves the fatty films that “blind” the turbidity sensor.
• Clean Your Filters Weekly: Most modern Frigidaires have a manual-clean filter at the bottom. If this filter is clogged, food particles circulate constantly, which can physically abrade or “sandblast” the plastic lens of the sensor, making it opaque over time.
• Check Your Water Temperature: Ensure your home’s water heater is set to at least 120°F (49°C). If the incoming water is too cold, detergents won’t dissolve properly, leading to the waxy buildup (soap scum) that coats the sensor and triggers the “tu” fault.
• Use High-Quality Detergent: Avoid “bargain” detergents that contain high levels of fillers. These fillers can settle on the sensor lens and cause false readings.

Frequently Asked Questions

**Q: Can I run the dishwasher while the “tu” error is active?**
**A:** Usually, no. Most Frigidaire models will lock out the control panel or refuse to start the wash motor when a turbidity sensor fault is detected. This is a safety and quality measure to ensure your dishes aren’t “cleaned” with stagnant, dirty water.

**Q: Is the turbidity sensor the same as the temperature sensor?**
**A:** In many Frigidaire models, they are integrated into a single “combi-sensor.” This is why a “tu” error is often accompanied by the water not heating correctly. When you replace the turbidity sensor, you are often replacing the thermistor as well.

**Q: Can I just bypass the sensor by jumping the wires?**
**A:** No. The control board expects a specific, fluctuating resistance and frequency from the sensor. A “jumped” wire would send a static signal that the board would recognize as an “implausible value,” resulting in a different error code or a permanent system halt.