QUESTION: I want to learn about stability control, which my new car supposedly has. How exactly does it work? How do I know what it is doing? Will it improve the way I can take corners?

–Paula H.

ANSWER: Electronic stability control, or ESC, has been available under many differing names for close to twenty years. Typically managed by the antilock brake control unit, in conjunction with other vehicle controllers and components, ESC helps bring a vehicle in line with what the driver intended. ESC is not intended to be a performance enhancement; it's there to help get you out of trouble as the vehicle becomes loose. Because of its proven benefits, ESC is now federally mandated on all passenger vehicles.

Several sensors are used, such as vehicle speed, yaw, steering angle and lateral acceleration. They determine the speed of each wheel; the degree of vehicle rotation, or turning; the driver's steering motions; and actual direction, which includes veering or sliding. Should the vehicle fail to turn in harmony with the driver's intentions, engine throttle is adjusted and individual wheel brakes are applied to straighten things out. Keep in mind that nothing can be done to overcome improper steering wheel actions, severe tire hydroplaning or the laws of physics.

You won't hear or see ESC activity until the car is pushed to a predetermined level of instability. An illuminated instrument panel lamp and/or tone will indicate ESC is intervening and the assistance may come in so smoothly, it may be difficult to determine how it is being done. I've noticed vehicles built perhaps 5-10 years ago intervened somewhat early and clumsily, seemingly scolding you with a large and lingering throttle reduction, while newer ones are smarter and take action more seamlessly.

I recently had the privilege of driving about two dozen new cars around Mazda Raceway in Monterey, Calif., and even under spirited cornering maneuvers didn't encounter a single ESC intervention. One explanation may be the excellent tires and suspension dynamics offered better grip than I felt comfortable exploring. In years past, the first thing one did when starting the car was to locate and press the ESC disable switch to avoid certain annoyance.

Q: I recently endured a problem with my car where the battery went dead while driving. It was the alternator that needed replacing. I was told if I had noticed the voltmeter reading incorrectly, I might have been spared the breakdown. How might this have looked on the meter?

–Raymond Peralta

A: While underway, a vehicle's charging system tries to maintain a system voltage of around 14-14.8 volts. When you see this on the instrument panel gauge, it's safe to assume electricity is being generated at a greater rate than is being consumed, and not in excess. At idle, with many accessory loads active, voltage may temporarily dip to perhaps 13-13.5 volts, as the charging system isn't as effective at low engine speed – but this is OK. A gauge reading below 13 or above 15 indicates a charging system fault. A low reading may lead to a discharged battery; a high reading may cook the battery and certain vehicle components.



Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at; he cannot make personal replies.


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