Under the Hood: Your car's engine can learn your ways
QUESTION: I 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 vehicle's 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?
ANSWER: Great question, John. My first experience with engine control memories was in the early 1980s with General Motors' 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.
Modern 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 facts afterward.
During a 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. It's a $700 part – 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 batteries.
With vehicles more sophisticated than mine, it's 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 operator's 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.
ABOUT THE WRITER
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at firstname.lastname@example.org; he cannot make personal replies.
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