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Saturday, October 27, 2012

How Does a Car Computer Work?


  • A car has at least one computer, but most have an engine control module (ECM), a body ride control unit, an ABS computer and a climate control computer. How many of these computers depend on the vehicle year, make and model and the options the vehicle has. If the vehicle does not have ABS brakes, it will not have an ABS computer. If the vehicle does not have climate control, it will not have a climate control computer.


  • The main computer is the engine control module. This may also be called the programmable control module. This computer takes its inputs and outputs through the various sensors on a vehicle. Sensors that give input give the computer information to send back to the engine via the output sensors.


  • Some of the sensors include a mass air flow sensor, a coolant temp sensor, cam sensor, crank sensor, idle air control motor, EGR valve, throttle position sensor and a knock sensor. Each sensor has its own job in telling the computer what the conditions are such as air quantity and quality, temperature of the coolant and where the throttle is. The computer uses this information to make infinite changes to the air-fuel ratio, turn the fans on or off and change the idle speed and injector timing, along with many other things needed to run the vehicle.


  • This part of the vehicle's running system is diagnosed by the engine control module. It lets you know when something is not working by turning the "check engine" or "service engine soon" light on. The ECM sends "codes" that turn the light on. A scanner is hooked up to the port under the driver's side dash so that the codes can be read. Because you cannot visually see if a sensor is bad, you must rely on the ECM to tell you this information. The scanner will tell you which sensor is out of range or not working at all.
    The ECM cannot diagnose itself. If an ECM goes bad, the vehicle may run badly or not at all. If the vehicle is running badly, a sensor could be out of range or bad, or the computer could be bad. When you hook up the scanner, you may get codes that do not exist or you may get codes that exist but do not make sense. This is a good sign that the computer itself is not working properly and should be replaced.


  • When you are working with the computer, extreme care must be taken. A friction shock from your fingers can damage the computer. Ground yourself before touching the computer. Most of today's computers must be programmed for the specific vehicle (getting "flashed"). You will need the VIN and the mileage of the car in addition to the numbers on the outside of the computer. The staffers at the auto parts store or the dealer should know that the PROM must be removed from the old computer and put into the new computer prior to "flashing" the computer. If they neglect to move the PROM or they say they will "flash" the computer without having your old computer, be sure to remind them that they cannot flash it without the PROM.

How to Build a Car Computer

Ryan Bauer
How to Build a Car Computer thumbnail
LCD touchscreen installation
Car computers, or "carputers" as they are often referred to, are essentially complete computers integrated into the interior of a vehicle. These multimedia systems put a multi-gigabyte collection of music at the driver's fingertips, as well as an assortment of tools such as GPS satellite navigation for trips and wireless Internet access that can be used when the vehicle is stopped. A regular car computer system will consist of two main components. The screen that is located in or on the dash provides the user with an interface to the computer. This is usually a touchscreen LCD. The other component is the actual computer itself, which is usually located in the trunk


    • 1
      Place the computer in the trunk of the vehicle. Any desktop PC will work for this purpose. To prevent the computer from sliding when the vehicle is moving, secure it to a fixed part of the car. One popular method for immobilizing the system is to connect it to the trunk's tie-down connectors using zip ties, wire, or a thin section of rope. One connection is enough to keep it from moving around if you locate the computer in a corner of the trunk.
    • 2
      Mount the touchscreen LCD in a place that will be easy to use but won't obstruct your vision while driving. If your screen fits the "double DIN" form factor, you can simply mount it where the stereo normally goes. Otherwise, it can be attached to the dash anywhere that is convenient. Use double-sided industrial strength adhesive tape or Velcro patches to hold the screen in place and keep it from moving.
    • 4
      While the carpet is still loose, now is the perfect time to run the power cord to the computer. Using a standard car stereo wiring kit, connect a positive line from the battery, through the firewall (using an existing wiring hole), along the side of the car under the carpet, and into the trunk. Tuck the carpet back into place under the trim. This positive power feed can then be connected to a DC-to-AC inverter to power the computer's existing power supply, or a replacement DC-to-DC computer power supply that eliminates the need for an inverter.
    • 5
      Connect the negative power connector of the inverter or DC power supply to a ground point on the car, preferably keeping the negative wire no longer than 1 to 2 feet in length. The most commonly used ground is the rear seat belt connector. Simply unbolt the seat belt from the car, file the metal to achieve a clean contact surface, and wrap the stripped end of the negative power wire around the bolt before replacing the nut.
    • 6
      Test the system. The computer can now be used just like any other PC would be. Use the system disk that came with the LCD to install the software that will allow the touchscreen to work. For sound output, hook an FM transmitter (these can be found for as little as $20 at any car audio store) to the audio output of the computer. This will allow you to tune your car stereo to a preset frequency (check the transmitter's manual) to hear sound from the car computer.


Car Computer History

Car Computer History thumbnail
Car Computer History
Computerized automotive systems are an ongoing evolution, continually improved from year to year to provide more efficient and more powerful cars. The basic fundamentals of the internal-combustion engine have not changed much since the beginning of the 20th century, but the need for tighter emissions standards coupled with fresh technology have made the on-board computer indispensable

Computers Come of Age

  • From the automobile's inception to the late 1960s, car engines were manufactured with simple designs and mechanical control parts, such as distributors and ignition timing controls. Emissions were not relevant, as efficiency gave way to horsepower and speed. As the 1970s began, federal mandates regarding a car's emissions were beginning to appear, and the fuel crisis of 1973 to 1974 showed many that larger and more powerful motors were not as important as economy. Most cars of this time period were fueled by carburetors, and very few ran with mechanical fuel injection, so the need for on-board computers evolved slowly. The actual physical requirements for an on-board computer had not been miniaturized to the point where they would fit into automobiles by the mid-1970s; it would take another decade before the microchip would be small enough to become practical.

Ignition Control Modules

  • As the gas shortages continued into the late 1970s, car manufacturers began to implement small, solid state circuit boards to control the ignition timing and spark, usually mounted into the engine compartment at the firewall. The hand-sized box would normally burn out within several years, requiring replacement. Several manufacturers experimented with computer-controlled carburetors into the early 1980s, using a crude microchip to meter the rate of fuel mixture and advancement of timing, but these proved unreliable and difficult to repair. The future of computer-controlled ignition resided in fuel injection, not carburetors, and through the middle of the 1980s almost all car makers pushed for an industry-wide changeover to integrated circuit controlled fuel injection.

Fuel Injection

  • The now complex carburetor gave way to fuel injection, mainly because of the ability of the computer to precisely measure the fuel into the engine. Carburetors had a number of disadvantages, such as vapor lock and altitude mixture problems, that a computer could solve with adjustments to the fuel injection system. As the microchip evolved, it became smaller and more powerful, and advancements in shielding could protect it from heat and moisture. Early automotive computers could be accessed with a standardized port in the dashboard, called OBD, or On-Board Diagnostics. This system utilized several sensors placed throughout the engine to relay problems to the technician, streamlining repairs.

OBD Comes of Age

  • As the 1980s gave way to the 1990s, on-board computers were deigned with more and responsibilities. Not only required to process the fuel mixture and timing, they now could be relied upon to control most of the electrical processes of the auto, including climate controls, braking systems and odometer. The computer became an integral part of the machine, upgradeable and customizable, giving the backyard mechanic incredible control over the powertrain's abilities. Using a laptop computer to interface with the OBD port, the programming of the car's microchips became second nature to racers. The engine's performance could be tweaked while the car was in use, and pertinent data could be relayed to the driver in real time. As the OBD system standard was improved upon, the OBDII, or OBD2 system was the next generation of auto computers. Powerful and malleable, this system eliminated the need to "sniff" tailpipes during emissions testing and allowed the sensors to relate the effectiveness of the emissions control systems.

Ghost in the Machine

  • In the beginning of the 21st century, computers become relied up to do much more than monitor and control the engine. With navigation systems, advanced climate controls, communications and entertainment devices, the on-board computer has become the most important part of the car's electrical system. Most automobiles have more computing power than a 1980's desktop computer and can monitor everything from coolant temperature to the ambient temperature of the interior cabin and make automatic adjustments. As vehicle makers improve on the internal-combustion engine, the future of the on-board computer is only just beginning; computers will be required in automobiles, gasoline powered or not, for decades to come.


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