McClatchy-Tribune News Service

QUESTION: I was told by a friend my newer car has something like 15 computers in it. Why so many? There’s no way the average car owner can fix their car anymore. Are the mechanics going to be able to fix them too? — Paula Warner

ANSWER: Depending on one’s definition of a computer we could bump your number as high as 50 on certain vehicles. I define it as a control unit containing a microprocessor, memory, diagnostics and/or communication abilities.

Electronic control units, or ECUs, manage a typical vehicle’s engine, transmission, brakes, climate control, instrumentation, restraint system, lighting, body functions — pretty much the entire car.

While this technology might seem intimidating, you end up with a smarter, more competent and reliable driving machine. Your computers check in with each other, share information and minimize the number of wires needed to control all the gadgets we’ve come to expect. As the vehicle awakes for use, ECUs test their communication ability as well as the wires connecting them. Should a fault exist, the ECU decides how to deal with the issue: Is there a way to work around the problem and maintain gadget functionality, or will certain features need to be suspended? Most faults result in an illuminated warning light and a diagnostic trouble code being set, which greatly speeds diagnosis and repair.

Vehicle speed is a good example of information being shared. Besides the engine and transmission ECUs needing to know your speed, other ECUs controlling instrumentation, cruise control, windshield wipers, audio system, even climate control want a piece of the action. Rather than have multiple sensors or wires zigzagging all over the place, the single sensor reports to one ECU and the information is broadcast on the same single or double wire carrying all other communication between units.

Power windows, door locks and mirrors are a good example of how wiring has been reduced. An older vehicle may have had more than 60 wires connecting to the driver’s door, each with the potential to break after flexing each time the door opens. Now, a module in the door interprets your switch selection and sends a signal through a single or double communication wire to another module much closer to the intended gadget, requesting operation. The very-low-current communication signals are hugely more reliable than an older circuit trying to muscle a function on its own from a distance.

Widespread ECU use has certainly changed the way cars are worked on. A pro-grade scan tool is essential to read codes, observe inputs, command outputs, run tests and validate successful operation after a repair is performed. At-home mechanics can still do their own vehicle maintenance, which has become simpler and easier than before, but an illuminated warning light will require a highly skilled tech with the right equipment and vehicle information to get the job done right on the first try.