Why Your Car Goes Crazy

Wacky behavior can usually be traced to overloaded microprocessors. That's a good reason to avoid fancy technology when car shopping

These days, more and more owners are complaining about a myriad of intermittent problems with their vehicles, and they range all over the spectrum. Sudden window openings, power-seat movements, engine shutdowns, navigation-system anomalies, transmission-shifting glitches, remote-locking-system failures, windshield wipers coming on, alarms engaging, and countless other operating deficiencies are reported around the country. Shop technicians seem unable to fix or even duplicate such symptoms when the vehicles are brought in for repairs.

So why is this happening? Well, according to John Hall, the main reason is that over the past 20 years the role of electronics in vehicles has moved from being "one of the band members" to being "the conductor." Hall is a expert in automotive electronics and has written a book called, Semiconductor Design & Implementation Issues in Integrated Vehicle Electronics. In it he explains that electronics -- specifically microprocessors -- now run your entire vehicle. These chips are everywhere in our lives nowadays. There's at least one in your microwave oven, TV, VCR, DVD player, etc., and a whole bunch of them in your car.

That's where the problem begins. The manufacturers have constantly strived to develop capabilities that large and varied populations will embrace and -- more important -- pay for. They've known for decades that fewer and fewer buyers will read complicated instructions for operating all the gadgetry, so the entire thrust of development is toward automated, "idiot-proof" features, and lots of them.


  The answer to the manufacturers' dilemma is the microprocessor. More to the point, it's the control module. This is a central "brain" built into the vehicle, and its job is to consolidate and control a variety of functions. In actuality, the control module (called many different names by individual manufacturers) is a bundle of chips all integrated into a central "command" unit. Individual devices that run, say, the windshield wipers or a four-wheel-drive transfer case, all "talk" to the control module, which allows the vehicle's electronics to handle many tasks at the same time.

Why do this, you might ask? Well, if you wanted to control each of a modern vehicle's electrical components individually any other way, you would have to "hard-wire" controls to every one of them and use a lot of switches. That would mean miles of wire and piles of other components for which there's simply no room, not to mention weight and cost concerns.

The microprocessor-packed control module is the solution. It becomes the "conductor" of the vehicle's "band." Unfortunately, the solution creates new opportunities for failure. One of these is the wiring that goes from the electronic devices to the control module. Wire is a great transmitter of electrical current, but it's also susceptible to high-voltage "spikes" from static discharges (lightning, high-voltage sources, shortwave radio, etc.) and can act like an antenna if not properly shielded.


  Another failure mode happens when the control module's microprocessors become overloaded with errant signals from any of the controllers or sensors that are connected to it. These devices are just as susceptible to outside electrical "noise" as the microprocessor itself, and it's nearly impossible to engineer around every potential failure or error in a cost-effective way. Military equipment is incredibly expensive because it's protected from such interference, but no one could afford an automobile with the same level of sophistication.

The reason your car might do weird things -- or do nothing at all -- is essentially the same reason your computer might or freeze. Lousy software design aside, computers and cars largely use so-called complementary-symmetry metal oxide semiconductors (CMOS) and similar devices. Any voltage surge (we're talking about very, very small voltages here) causes CMOS circuits to stop functioning until power is removed and reapplied. Once the fouled-up CMOS circuits are turned off and back on, they work fine and show no evidence anything ever failed.

Manufacturers use protection techniques to limit stray signals to electronic circuits. Resistors and diodes are added to circuits to filter incoming high-voltage signals, and the control modules themselves are packaged in interference-shielding materials.


  However, vehicles still have lots of wiring in them, and any single wire on any day can suddenly become an antenna that's tuned precisely to some stray electromagnetic signal. Under the right circumstances, a policeman's radio, a CB radio, a microwave tower, or even a customer sliding over the seat can generate a high static voltage spike that results in a momentary, erratic signal to the vehicle's control module. This can result in one of innumerable things going wrong. (By the way, that spark you get when you touch a switch plate on a winter's day has between 2,000 to 3,000 volts -- more than enough to throw off your car's electronics!)

The problem is that many of these symptoms can't be traced by even the most competent technicians at the shop level, thereby leading owners to conclude that they have a "lemon." In addition, many problems can occur after sound systems or other aftermarket electronics have been installed in vehicles because the wiring integrity has been compromised. That's why dealerships are telling customers not to install devices that haven't been certified by vehicle manufacturers.


  Eventually, the state of the art in electronic design will catch up with, and solve, the potential for freezes and false signal failures in vehicles. Until then, the best protection for consumers is to avoid cutting-edge technology features in new vehicles.

Among those to avoid now include: active suspension, iDrive type systems, and keyless ignitions. Basically, anything that's going to cost a lot of money to fix outside of warranty should be strongly considered before buying. Such gadgetry can disable the vehicle when it fails. Wait a few years for these devices to get the bugs ironed out and for them to become reliable, mainstream features.

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