Q. I was hoping you could shed some light on a couple of new razzle-dazzle items appearing on my favorite cars, namely stability control and throttle-by-wire. How do they work? Are they trustworthy? After living with a half-dozen check-engine lights over the past decade, I’m not sure I’m ready to trust important stuff like this to some egghead beneath the dashboard.

Michael Holland,

Columbus, Ohio

A. I don’t blame you for wondering about a system that can strongly influence how your car takes a corner or accelerates. Let’s look at how these systems work and the safeguards used to prevent improper operation.

Electronic stability control systems integrate anti-lock brake and traction-control system components that are already in place, along with a few new parts and clever software to help keep your car on course during to-the-limit cornering maneuvers.

Sensors for steering wheel position, yaw (rate of turn) and lateral acceleration (sideways movement) are used to detect the vehicle’s intended and actual rate of turning. If excessive understeer (the front wheels are plowing ahead rather than turning) occurs, the inboard front brake is applied, via the anti-lock brake system, along with any needed adjustments to vehicle power. This encourages the vehicle to pivot slightly around the “planted” wheel’s axis, helping to make the desired turn.

In an oversteer condition (the rear swings out), the outboard wheel is braked, causing the opposite effect. Some vehicles also might apply braking force to individual rear wheels to keep you safely on course.

In the event a sensor, actuator or circuit fault occurs, the system will stop operating – restoring traditional driving function – and illuminate a warning lamp.

All it took were two or three passes through a wet test track – with the system active, then turned off – to make me a believer in its smooth and intuitive functions.

Let’s look at Honda’s electronic throttle system, which improves fuel economy, reduces emissions, improves transmission shifting and eliminates the need for idle speed, fast idle and cruise-control actuators.

Rather than using a traditional mechanical cable to connect the accelerator pedal and cruise-control actuator to the engine throttle, two accelerator pedal position sensors provide the ECM/PCM (engine/powertrain control computer) desired throttle position.

The ECM/PCM then sends a command to the throttle actuator module, which in turn sends a series of electrical pulses to a reversible electric motor built into the throttle body.

As the motor moves the throttle, two throttle-position sensors provide feedback to the ECM/PCM for refinement and diagnostic purposes.

The system tests itself continuously, and in the rare case a fault were to occur, it ceases operation, allowing a powerful spring to return the throttle to a tepid, but surprisingly drivable part-throttle position.

Brad Bergholdt teaches automotive technology at Evergreen Valley College in San Jose, Calif.

E-mail him at under-the-hoodjuno.com or write to him in care of Drive, Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190. He cannot make personal replies.)

—

(c) 2004, San Jose Mercury News (San Jose, Calif.).

Visit MercuryNews.com, the World Wide Web site of the Mercury News, at http://www.mercurynews.com.

Distributed by Knight Ridder/Tribune Information Services.

AP-NY-08-06-04 0618EDT