Page 106 - Toyota Under Fire

THE RECALL CRISIS

FIGURE 3.1 TOYOTA FAIL-SAFE ELECTRONIC
THROTTLE CONTROL SYSTEM

Throttle Position
Sensors
Inputs from two different
position sensors are
monitored and compared
for abnormalities by CPU.

Inputs from two different
position sensors are
monitored and compared
for abnormalities by CPU.
Accelerator Pedal
Position Sensors

Two CPUs monitor the
operations of each other.
Control CPU
monitors
motor drive current.

These fail-safe systems to prevent errors in the sensors have
worked exactly as expected in testing and on the road. But the
vulnerability of electronic systems isn’t limited to errors and com-
ponent failure; these systems are also vulnerable to interference.
Any electronic signal can be disrupted or altered by electromag-
netic radiation, referred to as electromagnetic interference, or
EMI. If you’ve ever heard the distinctive tapping sound when
a cell phone gets too near a landline telephone or a speaker,
you’ve experienced the effects of electromagnetic radiation. Ve-
hicle manufacturers obviously have to protect their ECMs and
electronic throttle controls from EMI. Kristen Tabar, general
manager of electronic systems at the Toyota Technical Center in
Michigan, explains how all manufacturers’ vehicle electronics are
rigorously designed to protect the systems from EMI:

75