Networking for your car
by Jim Kerr

Networks are all around us. The banks are networked so you can access your funds almost anywhere. Telephones have a huge network! And even people network to benefit mutually from each others experience and expertise. Now our cars are becoming progressively networked, and they are performing tasks easier and quicker than ever before.

There are many vehicles sold that have some computer networking. It is sometimes called multiplexing. One of the latest cars on the market, the 2001 Oldsmobile Aurora, is a perfect example of how cars are working better with network technology. The Aurora may have twenty-one or more computers and modules on board, all connected together to make our life easier and the car safer.

However, before we look at the Aurora, a little history may help us understand the benefits of networking. Computers became common on cars when fuel injection was introduced in the 1980's. These early computers were very simple and had very few inputs. Soon afterwards, body computers wee designed into a few luxury cars. These body computers monitored and operated the lights, alarm systems, and door locks, as well as a few other convenience features.

Then came Anti-lock brakes, with another computer, and airbags with another computer, and automatic air conditioning, and ride control systems, an on and on and on! Each computer was wired to sensors, switches, and relays located all over the car and the wiring harnesses became extremely complicated and large. It was common to have over fifty different wires running the full length of the car. Diagnosing an electrical problem was enough to turn your mechanic's hair grey! It was time for a better system.

The 2001 Aurora uses many computers networked together to operate the convenience and safety features of the car.

Networking on the 2001 Aurora is done with communications data lines that link all the computers together. Each computer or module is supplied battery power, ground, and the data line. Some of the computers have input connections to sensors and switches, and some control relays and motors, but the number and length of wiring used is now significantly smaller.

Let me give you an example of how it works. The remote trunk release switch on the driver's door is wired to the driver's door module. Press the switch and the door module sends a data signal to the Rear Integration Module (RIM), located in the trunk. The RIM checks data signals from other computers to see if the transmission is in Park, or the engine is not running, and then it operates a relay to energize the trunk release solenoid and the open the trunk lid!

Now this may seem to be a little excessive just to open the trunk, but the same method can be used for other features. The door jamb switch that used to operate just the interior lights, now has its door open signal sent to every computer in the car. Depending on other signals, one computer may use it to turn on the interior lights (if it is dark!), another to turn off the radio, and another to trigger the alarm system.

Two features of the Aurora that fully utilize the network are driver personalization, and On Star. When a driver sets the controls the way they desire, the personal settings are remembered in each computer. When the driver unlocks the car with the keyless entry, or presses the memory seat button, all the computers reset the controls for that driver. The seat and mirrors adjust, the door locks operate as programmed, the radio station sets the station, volume and presets, and the air conditioning turns on just as you left it.

When the other driver uses their keyless entry fob to unlock the car, all the controls are reset for the second driver! This is all done with data communication between the many computers and this level of personalization would be extremely complex without networking.

On Star, the General Motors cellular communications network, extends the car computer network to the outside world. Press a button and On Star calls the GM assistance centre. Using the car's global positioning sensor, the operator can tell where your Aurora is and direct you to the nearest service depot, gas stop, or restaurant! If your vehicle is not operating properly, they can get data from the computers and tell you what you should do. They can even send a tow truck if required!

Safety is a big part of the On Star system. If an air bag goes off, the system sends out a priority code, and the assistance centre will try to contact you. If there is no answer, they will send out emergency vehicles directly to your location!

If you lock your keys in the car, phone the On Star centre. Give them your password, and they can send a phone message to your car. The phone module then sends a data signal to the other computers to unlock the car; all through the miracle of computer networking.

Networks of some type will soon be found on almost all cars. The amount of wiring on the car is reduced, and the features available are limited only by the designers imagination. So how will they be to repair?

Technicians who have worked on these type of systems find them much easier to diagnose and repair than older systems. They can connect in a hand held diagnostic computer to the network and much of the work can be done from the driver's seat!

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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