Page 103 - Toyota Under Fire

TOYOT A UNDER FIRE

systems. In an all-mechanical system, a cable or a set of rods con-
nects the accelerator pedal to the throttle of the engine, which
governs how much air enters the engine’s combustion chamber.
With electronic throttle control, a sensor monitors the position
of the gas pedal and transmits that information “by wire” (which
is why they are often referred to as “drive-by-wire” systems) to the
ECM, which then sends a message to the electronic throttle con-
trol that tells the throttle to let more or less air into the engine’s
combustion chamber.
As with any system that relies on moving parts, there are
downsides to the old-fashioned mechanical throttle control: cables
can become stretched or brittle; rod couplings can become worn
and loose. Mechanical systems also have limited precision. But
most important of all, mechanical systems are “dumb”; the sys-
tems can’t communicate with one another. An electronic throttle
control system coupled with the other computers in the engine
and transmission allows for fine-tuning of performance depend-
ing on exactly what the situation is. For instance, the use of elec-
tronic throttle control, ECMs, and other computers has produced
some of the most important safety advances in the last decade,
features like stability and traction control. Other computers in the
car are responsible for antilock brakes and air bags. Without
the use of computers, these features would literally be impossi-
ble. These computer-driven safety features are largely responsible
for the fact that traffic fatalities in the United States in 2009 were
at the lowest level since 1950.
But unlike mechanical systems, electronic systems carry
some mystery about them. There’s a general belief that if they
malfunction, you can’t necessarily see what went wrong the
way you can with a mechanical system. According to Jeremy
Anwyl, CEO of Edmunds.com, one of the leading automotive-

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