What’s All This About a Computer in My Car?

The “Computer” in Your Car Doesn’t Have a Screen, a keyboard, or a Disk Drive — but It’s Got Lots of Connections.

Your car’s on-board computer doesn’t look anything like the kind that’s used on a desktop. The “computer” is a small box called an ECM (Electronic Control Module), often mounted behind the glove box or in the engine compartment. The ECM controls all the essentials of engine operation: spark timing, fuel delivery, emissions, and in some cases even the air conditioning or the automatic transmission. Keeping all those systems in tip-top shape is no simple job; it requires complex test equipment and advanced diagnostic skills.

The computer continuously receives electrical signals from sensors and input devices, located in and around the engine. It analyzes this information and sends a stream of control signals to valves, controllers and other output devices, to balance the requirements of power, fuel economy and emission control. Some of the most common devices are shown in this brochure. Every engine, every car and every computer system is different — but all the sensors, all the output devices, must be in perfect “sync” for the car to run properly.

No system is foolproof. When problems develop, the malfunctioning parts must be replaced or adjusted. Otherwise the car won’t run right, the gas mileage will be poor, and the car won’t pass an emissions inspection. Only a qualified technician, with the right diagnostic equipment and technical data, can find out what’s wrong and restore your car to original performance specifications.

Watch For These Warning Signs That Tell You Your Vehicle Needs Service