QUESTION: 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.
—Kelsey Pooler
ANSWER: 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, such
as a single irrational sensor, 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. Fuel delivery, ignition timing, and/or
valve operation may also be manipulated to allow
alternatively controlled engine operation.
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.
———