have written before concerning a problem I had with my truck, and
your repair suggestion was right on the money. I now have a question
about something you mentioned in a recent column. In the article,
you referred to a vehicleís learned values for engine management.
Would you mind expanding on that? Do these computers actually learn
over time? How long does it take them to learn? What do they learn?
Are they in all recent models?
question, John. My first experience with engine control memories was
in the early 1980s with General Motorsí Computer Command Control
system. Besides recording faults and setting trouble codes for later
retrieval, the fuel injection system was smart enough to keep track
of the amount of correction necessary to keep the exhaust oxygen
sensor happy and apply the correction the next morning, even before
the sensor woke up. This did wonders for cold engine drivability.
The system also proactively corrected fuel delivery under all
operating conditions, providing sweet and efficient performance. The
control computer, called an ECM back then, also needed to keep an
accurate memory of the idle control stepper motor position, or idle
speed would become very wrong.
vehicles go far beyond these baby steps, learning operator behavior,
degraded component characteristics and environmental conditions,
among other things. With advances such as electronic throttles,
variable valve timing, variable geometry turbochargers and
electronically shifted transmissions, system tracking and
corrections constantly occur. These can be proactively applied to
smooth performance, reduce emissions and stretch every drop of fuel.
Many transmissions observe vehicle behavior when climbing a long
hill and apply logic toward what may lie ahead. Shifts are also
sweetened, based on earlier behavior, thanks to clutch or fluid
irregularities. Air bag systems can also store "black box"
information preceding a crash/deployment to assist in compiling
recent icy-cold morning startup in the High Sierras, my Silverado
battery voltage dipped a bit low while cranking. The diesel engine
started, but I was rewarded with an illuminated check engine light
among other issues. After returning home I retrieved codes and
discovered a startling batch of them including multiple
communication errors and the dreaded turbo vane position sensor
code. Itís a $700 part ó yikes. Thinking it odd the codes all
set immediately after the slow crank, I cleared them, and they have
never returned. Just a momentary loss of memories had occurred, but
it was enough to cause all this plus wipe out radio stations, clock,
memory seat positions, and emissions monitors. The truck relearned
the needed engine, emissions, transmission and transfer case
memories within an hour or so of driving, the control modules all
shook hands successfully, and I reset the others. Time for two new
more sophisticated than mine, itís certainly likely that
professional service may be needed to perform relearn procedures in
the event of a dead or disconnected battery. In addition, I would
never, ever jump-start a modern vehicle without first consulting the
operatorís manual for any special concerns and being absolutely
sure of proper cable polarity. Most relearning can occur fairly
quickly, if the right operating conditions are presented or are
initiated using a scan tool.