DIAGNOSIS: That's the tool's fault indicator. A blinking red/green light sequence means it's detecting an internal problem—often an overheated motor, a faulty switch, or a communication error with the battery.
FIX: First, let it sit for 30 minutes to cool down completely. Try a different, known-good 20V MAX battery. If it works with a different battery, the first battery might be faulty or have dirty terminals. Clean all battery and tool terminals with a dry cloth.
IF THAT DIDN'T WORK: If the problem persists with multiple good batteries, the issue is inside the tool. The most common culprits are the trigger switch or the electronic control board. Both require disassembly and component-level testing/replacement.
HEADS UP: This isn't a user-resettable error like some tools have. If cleaning and a battery swap don't fix it, it needs professional diagnosis. Don't keep pulling the trigger hoping it'll clear.