LG Dryer Moisture Sensor Replacement — Fixing Auto-Dry Problems
LG dryers use two types of sensors that get confused in conversation: the moisture sensor bars inside the drum and the exhaust thermistor near the vent. They do completely different things, fail differently, and have different replacement procedures. If your LG dryer over-dries or under-dries on auto-dry cycles, understanding which sensor is at fault saves money and frustration.
Moisture Sensor Bars vs Exhaust Thermistor
Moisture sensor bars: Two parallel metal strips mounted inside the drum, usually near the lint filter housing. As wet clothes tumble and contact these bars, they complete a low-voltage circuit. The resistance between the bars changes with fabric moisture level. When clothes are wet, resistance is low. As they dry, resistance increases. The control board uses this reading to determine when to end the auto-dry cycle.
Exhaust thermistor: An NTC temperature sensor mounted in the exhaust duct or on the blower housing. It measures the temperature of the outgoing air. Hot, dry exhaust air indicates dry clothes. This provides a secondary drying signal that supplements the moisture bars.
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Multimeter ($85), vacuum pump ($250), diagnostic software, and specialized hand tools. Our technician arrives with $15K+ in professional tools — your diagnostic is free.
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Symptoms by Sensor
| Symptom | Sensor | Fix |
|---|---|---|
| Auto-dry stops too early, clothes damp | Moisture bars coated with residue | Clean bars with rubbing alcohol |
| Auto-dry runs forever, clothes over-dried | Moisture bars shorted or thermistor failed | Test and replace |
| Timed dry works fine but auto-dry does not | Moisture bars or thermistor | Test both |
| Error code related to temperature sensing | Exhaust thermistor | Test resistance |
The Dryer Sheet Problem
The most common moisture sensor issue is not a failed sensor — it is dryer sheet residue coating the sensor bars. Dryer sheets deposit a waxy film on everything they touch, including the metal sensor bars. This film insulates the bars from wet fabric, making the board think clothes are drier than they are. The auto-dry cycle ends prematurely.
Fix: Clean the sensor bars with rubbing alcohol and a soft cloth every month. Locate them inside the drum near the lint filter — they look like two thin metal strips running parallel, about 4-6 inches long. This free fix resolves 70% of auto-dry complaints.
Safety First — Know the Risks
Appliances involve high voltage (120-240V), pressurized water, gas lines, and chemical refrigerants. Over 400 DIY repair injuries are reported yearly. Our techs are licensed and insured — let them handle the risk.
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Part Numbers and Pricing
| Part | LG Number | Price |
|---|---|---|
| Exhaust thermistor | 6931EL3003D | $12-$40 |
| Moisture sensor bar assembly | Varies by model | $15-$45 |
| Aftermarket thermistor | Various | $8-$20 |
| Professional diagnosis + replacement | — | $90-$160 |
Testing the Exhaust Thermistor
Disconnect power. Access the thermistor from the rear panel or through the lint duct area. The thermistor is a small component with a 2-wire connector.
Disconnect the wires. Measure resistance at room temperature — expected reading is approximately 10K-50K ohms (varies by model). At operating temperature (150F+), resistance should drop to 1K-5K ohms. Infinite resistance = open (failed). Zero resistance = shorted (failed).
The Real Cost of DIY
Average DIY attempt: $150-400 in tools you may use once, plus the risk of further damage. Our diagnostic visit costs $0 — we find the problem and give you an honest quote.
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Testing the Moisture Sensor Bars
With the dryer off, use a multimeter to measure resistance across the two sensor bar terminals (accessible from behind the front panel or at the control board connector). The bars should read open (infinite) when dry and clean. Lay a damp cloth across both bars — resistance should drop to a few thousand ohms. If resistance does not change with moisture, the bars or their wiring have failed.
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Tools Required
- Multimeter — essential for both sensor types
- Phillips #2 — for panel access
- Rubbing alcohol and soft cloth — for sensor bar cleaning
Don't Void Your Warranty
Opening your appliance yourself may void the manufacturer warranty. Our repair comes with a 90-day guarantee, and we document everything for warranty compliance.
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Replacement Procedures
Thermistor: Access from rear panel. Unplug connector, remove mounting clip or screw, install new thermistor. 10-minute job.
Moisture sensor bars: These mount inside the drum through the front bulkhead. Access requires removing the front panel and sometimes the drum. Remove the old bar assembly mounting screws, disconnect the wire leads, and install the new assembly. More involved than the thermistor — 45-60 minutes including disassembly.
Frequently Asked Questions
My LG dryer on auto-dry stops before clothes are fully dry. What is wrong?
Clean the moisture sensor bars inside the drum with rubbing alcohol first — dryer sheet residue is the most common cause. If cleaning does not help, test the exhaust thermistor resistance.
Can I use timed dry instead of fixing the sensor?
Yes, timed dry bypasses the moisture sensors entirely. But you lose energy efficiency — timed dry runs for a fixed duration regardless of whether clothes are already dry, wasting electricity.
Are LG dryer moisture sensors covered under warranty?
Sensors are covered under the standard 1-year warranty. They are not included in the 10-year Direct Drive motor warranty.
LG dryer auto-dry not working? Our technicians clean sensor bars and test thermistors on every service call. Book a technician →
