The year 1970 was a pivotal one for the U.S. auto industry. With new car designs already on the assembly lines, Congress threw automakers a curveball by passing the Clean Air Act and establishing the Environmental Protection Agency (EPA). Thus began a series of new federal emissions standards and maintenance requirements that would gradually roll out over the next decade.

Because of these progressively rigid standards, automobiles needed to become more sophisticated. Manufacturers started installing electronic computer controls on their vehicles to monitor engine functions and diagnose engine problems. This On-Board Diagnostic (OBD) system was necessary to keep everything performing properly and to alert the driver when it was time to seek the aid of a mechanic.

In the '90s, the feds buckled down even further, requiring that all cars and light trucks sold in the United States after January 1, 1996, be equipped with more-sophisticated OBD II monitoring equipment and a built-in diagnostic port. This port--typically referred to as the ALDL, or "Assembly Line Diagnostic Link"--is used for retrieving powertrain information with a scan tool.

To ease the diagnostic process, federal regulations dictate that the ALDL must be located within three feet of the driver and that it not require any tools to be accessed. When an OBD I or OBD II system detects a powertrain problem, it logs it as a fault code in the vehicle's computer memory. When retrieved, this code provides information regarding the source of the trouble.

The EPA estimates that more than 6 million Americans are currently driving cars with a "check engine" or "maintenance required" light illuminated. The cause could be as benign as a loose gas cap or as serious as an internal powertrain problem. Being able to quickly retrieve and interpret the fault code(s) behind that check-engine light could get you back on the road in a few minutes or even save your engine.

As mentioned earlier, you can use a scanner to retrieve codes via the vehicle's ALDL. Scanners can be costly to purchase and maintain however, and are therefore typically purchased only by mechanics. Fortunately, there is a way for you to find the codes in the computer's memory by using the programming buttons on your dashboard. The following directions will guide you through this easy task.

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You can enter the Diagnostic Display mode using the following procedure:
1. Turn the ignition to the "On" position but don't start the engine.
2. Press the "Reset" button on the Driver Information Center (DIC) to turn off any existing warning messages.
3. Press and hold the "Options" button.
4. While holding the "Options" button, press the "Fuel" button four times within a 10-second period.