Electronic throttles have good record

Q: This latest talk of electronics problems on Toyotas has me creeped out even more than before. I was considering the purchase of a new Lexus but am now afraid to pull the trigger. Any light you could shed on this would be appreciated.

A: It's been a while since we looked at electronic throttle control (ETC), so perhaps we could do so again. ETC has been around for quite some time and is also used in big trucks, heavy equipment, and airplanes. Getting rid of the mechanical connection between one's foot and throttle sounds a little scary, but when it's done right (as it is), the chances of a problem are minuscule, and the benefits are many.

ETC allows more precise throttle control, improving fuel economy. ETC makes it possible for the vehicle's stability and/or traction control systems to reduce throttle from that requested, in order to regain or enhance vehicle control. What's more, it eliminates the need for idle speed and cruise control actuators, saving weight, complexity and cost.

ETC systems typically employ a pair of pedal position sensors attached to or near the accelerator pedal. The sensors are wired opposite of each other, or operate at differing voltages, so should an electrical fault such as excessive resistance, a short, or open circuit develop in the either of the sensors or wiring, it's easily recognized rather than misinterpreted. Sensor information is received by the powertrain control module (PCM), processed for rationality, and acted upon via commands to an electric motor attached to the throttle. This side of the system is also designed carefully. The motor requires not one, but two precise electrical signals to operate, and double/opposite throttle position sensors indicate true throttle position.

Should a manageable fault occur, the system will reduce available throttle dramatically or completely and illuminate the check engine light. A more severe fault will result in complete suspension of throttle operation. In this case a strong spring in the throttle assembly forces the throttle to about 6 percent opening, so the vehicle can be limped safely to the side of, or off the road.

Concerns of electromagnetic interference affecting vehicle electronics have now surfaced. Electromagnetic interference is caused by a rapidly changing electrical current and can occur from sources inside or external to the vehicle, possibly affecting system operation. This is troubling, as the problem has many possible sources and doesn't leave any fingerprints for subsequent diagnosis. My experience with vehicle electronics, dating back to the 1980 Chevy Citation (a check engine light magnet), gives me confidence in the robust EMI suppression strategies used by all carmakers. The vast majority of the problems I've encountered have had a verifiable cause, and it wasn't EMI. You're more likely, I believe, to have a wheel fall off, than to encounter a serious EMI-caused problem.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him e-mail at under-the-hood@earthlink.net; he cannot make personal replies.