A powerful computer controls a broad range of
functions throughout your car's engine and power train. This on-board computer uses an
extensive set of sensors, located throughout the automobile, to closely monitor
systems operation many times each second. This computer engine control system was
originally designed to enable automobile engines to meet air pollution standards
established by the Environmental Protection Agency (EPA) and the
Resources Board (CARB) while increasing automobile fuel efficiency.
To affect engine operation, the
computer controls devices, called actuators, such as fuel injectors, idle air
control, exhaust gas recirculation (EGR) valves, and the ignition module. To
help reduce air pollution, it also monitors and records information related to engine
emissions. When certain problems are detected, the system lights the Malfunction
Indicator Lamp (MIL) and records Diagnostic Trouble Codes
sold in the United States since 1996 are required by law to include a computer control
system meeting requirements known as On-Board Diagnostics, Generation Two, or OBD
II for short. These cars have a standard electronic cable connector, often
located under the dash near the steering column. Various devices, called
code readers or scanners, can be plugged into this
connector to read the diagnostic scan codes, and also turn off the MIL.
The “Malfunction Indicator
Lamp” (MIL) is the accepted term used to describe the lamp on the dashboard that
lights to warn the driver that an emissions-related fault has been found. Some
manufacturers may still call this lamp a “Check Engine” or “Service Engine Soon”
After the MIL has
been turned off, DTCs, Freeze Frame data, and manufacturer-specific enhanced
data stay in the computer’s memory. Most of the enhanced data can only be
retrieved with special equipment such as a Scan Tool.
The diagnostic trouble codes give important clues
about the particular failure that caused the MIL to light. Often these trouble
codes can lead a skilled person to a successful repair
of the problem.
Fix any known mechanical problems before
performing any test. See your vehicle’s service
manual or a mechanic for more information.