Diagnosis
The moisture sensor is blocked by lint. The 'Check Filter' message is often a misnomer. It triggers when the sensor can't detect humidity changes.
How to Fix It
Unplug the dryer. Pull the lint filter out completely. Use a vacuum hose to clean deep inside the filter cavity. Wipe the moisture sensor bars inside the drum with rubbing alcohol. They're the two thin metal strips near the front. Let dry, plug back in.
If That Didn't Work
Check the external vent duct. A severe blockage there can also cause the error. Disconnect the duct from the back of the dryer and ensure air flows freely outside.
Heads Up
Do not ignore this error. Running the dryer with a blocked sensor or vent can overheat components and is a fire hazard.