Advances in vehicles today are often only possible with the integration of computer technology. At least one computer, microprocessor, or electronic control module provides accurate and instant commands to almost every major mechanical or electrical system (e.g., ignition, fuel, emission, transmission, brake, safety restraint, navigation, and traction control).

Powertrain Control Module. The main computer is commonly called the engine control unit (ECU), electronic engine control (EEC), electronic control module (ECM), or the powertrain control module (PCM). PCM is the standardized name used by the Society of Automotive Engineers and will be used throughout this book. Sensors are constantly inputting raw information, in the form of electrical signals, into the PCM where the data is analyzed, processed, and sometimes stored. The type and number of sensors and computers on vehicles vary. Computers monitor and adjust engine controls by performing self checks to make sure the engine is running efficiently.

On-Board Diagnostics. When something is not working properly a trouble code will normally be stored in the computer. The check engine light will go on if a code is stored. A scan tool is used to retrieve stored on-board diagnostics (OBD) codes. Most computers never need maintenance, but if they fail they will need to be replaced. Often the problem is sensor input. If you are having trouble with diagnosis take your vehicle to the dealer. A computer is covered under an extended federal emission warranty.