Diagnosis
The tool's onboard computer is detecting a fault. This is usually an overload/overheat lockout or a communication error with the battery.
How to Fix It
First, perform a hard reset. Remove the battery. Hold the trigger down for 30 seconds. Reinstall the battery. If it works, the thermal protector just needed to reset. If it still blinks, try a different, known-good LXT battery. This isolates if it's the tool or the battery.
If That Didn't Work
The problem is in the tool's control board. Moisture or conductive dust can cause a short, triggering the fault light. The board would need replacement.
Heads Up
Do not try to bypass this protection. The red blink is preventing a potential fire or motor burnout from a short circuit. It's a critical safety feature.