Samsung Dishwasher: Replace Turbidity Sensor

What the turbidity sensor does#

The sensor shines an infrared beam through the circulating water and reads how much reaches a photodiode on the far side. Clear water lets the light through and tells the board the dishes are clean, so it moves to rinse; dirty water blocks the light and the wash continues. It sets the length of Auto and Smart cycles, so when it fails those cycles run far too long or far too short. It is a separate part from the thermistor that measures water temperature.

Safety warning: Disconnect power at the circuit breaker. The sensor uses low-voltage signaling but is located near high-voltage heating element connections. Always verify power is off before reaching into the sump area.

Confirm the sensor is the fault#

• An Auto cycle that used to run around an hour and a half now runs past three hours: the sensor reads dirty water constantly.
• Auto ends in half an hour with dirty dishes: the sensor reads clean water immediately.
• Normal and Heavy cycles work but Auto does not: those use fixed timing, so a sensor-only fault shows up only on the sensor-driven cycles.
• A film of grease or scale on the lens can mimic all of the above, which is why you clean it first.

What you need#

Step by step#

1 - Cut power and open the interior. Trip the breaker, then pull the lower rack, twist off the lower spray arm, and lift out the coarse and fine filters to expose the sump.

2 - Find the sensor. Look into the sump for a small cylindrical part, about the size of a large marble, set in the sump wall with a clear lens facing the water — usually toward the back-left, away from the drain opening, on a two-wire connector.

3 - Clean the lens first. Wipe the clear lens with a soft cloth, warm water and a drop of dish soap, since scale or grease film reads like dirty water. Refit the filters and arm, restore power, and run an Auto cycle with a light load — if it finishes in normal time, you are done.

4 - Reach the wiring. If cleaning did not help, take off the kick plate (two screws and two clips) so you can reach the sensor's two-wire connector from below, and press its tab to unplug it.

5 - Release the old sensor. Samsung mounts it one of three ways: a twist-lock that turns about a third of a turn and pulls out, a clip you depress with a flathead while pushing the sensor into the sump, or a single screw on a bracket. Note how deep the lens sat in the flow before pulling it.

6 - Check the hole and fit the new sensor. Clear scale from the mounting hole and check the grommet or O-ring, then insert the new sensor lens-first into the flow at the same depth and secure it by its mount. The lens must sit in the moving water to read correctly.

7 - Reconnect, reassemble and test. Click the connector back together, route the wires clear of heat and moving parts, refit the filters (fine first), the spray arm and the rack, restore power, and run an Auto cycle with a light, lightly soiled load — a return to a normal-length cycle with clean dishes confirms the fix. Refit the kick plate.

When to call a professional#

Bring in a technician if the mounting hole in the sump is cracked and leaking, if the Auto timing is still wrong after a new sensor (a board-logic issue), if you cannot locate the sensor in the circulation path, or if several sensors fail at once.

Need professional help?#

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