The ABS module is the brain of a Porsche 911's anti-lock braking system and regulates brake pressure to prevent wheel lockups. A bad ABS module can cause issues like a blinking ABS light, locked brakes during braking, an unresponsive brake pedal, and inaccurate speedometer readings, putting the braking system and safety at risk. Symptoms of a faulty ABS module include damaged wiring, contaminated sensors, blown fuses, electrical shorts, or power surges. It is important to check the ABS control module and replace it if necessary.