Electronic Stability Control

Electronic Stability Control — ESC, also called ESP, DSC, VSC, or StabiliTrak depending on manufacturer — is the most significant safety advancement in vehicle dynamics since the seatbelt. It detects when the vehicle is beginning to skid and applies individual wheel brakes to correct the skid before the driver even realizes what is happening. Federally mandated on all passenger vehicles sold in the United States since model year 2012.

ESC uses all four wheel speed sensors from the ABS system plus two additional sensors. The steering angle sensor measures exactly where the driver is pointing the steering wheel — it tells the module what direction the driver wants to go. The yaw rate sensor measures the actual rotational motion of the vehicle around its vertical axis — it tells the module what direction the vehicle is actually going. A lateral accelerometer measures side-to-side g-force. When there is a difference between where the driver is steering and where the vehicle is actually going, the vehicle is in a skid. ESC intervenes.

Two types of skids exist. Understeer — the front tires lose grip and the vehicle pushes wide, going straight instead of turning. Oversteer — the rear tires lose grip and the back end swings out, spinning the vehicle. For understeer, ESC applies the inside rear brake. This creates a yaw moment that helps rotate the vehicle into the turn. For oversteer, ESC applies the outside front brake. This creates the opposite yaw moment that slows the rotation and straightens the vehicle. Simultaneously, the module reduces engine power to slow the vehicle and help the tires regain grip. All of this happens in milliseconds, often before the driver feels the skid begin.

The steering angle sensor must know the exact center position of the steering wheel to calculate the driver's intended direction. Most vehicles self-calibrate the sensor during a specific drive procedure — turning the wheel lock to lock and then driving in a straight line. After an alignment, a steering column repair, or any work that changes the steering wheel position relative to straight-ahead, the steering angle sensor must be recalibrated. An uncalibrated sensor means the ESC module has incorrect data about the driver's intended direction. The system either intervenes inappropriately or fails to intervene when needed. Calibration requires a scan tool on most vehicles.

ESC reduces single-vehicle crashes by approximately 50 percent and SUV rollovers by approximately 80 percent according to NHTSA data. Those are not small numbers. That is a system that cuts your chances of a deadly crash in half. The only legitimate reason to disable ESC is sustained off-road driving or drag racing. For any normal street driving, including performance driving on public roads, leave it on.