If the emergency lights (hazard lights) come on when you step on the brake in a 2001 Chevy Venture, it almost certainly indicates a problem with the brake light switch. This switch is responsible for turning on your brake lights when you press the brake pedal, and a faulty switch can cause a variety of issues, including inadvertently activating the hazard lights.
Other less likely possibilities include a short circuit in the wiring related to the brake lights or hazard lights, but the brake light switch is the most common culprit. You should have a mechanic inspect the brake light switch and wiring. Driving with this problem is unsafe as it could confuse other drivers and lead to an accident.
