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1 EMISSIONS AND OBD II on Wed Jul 20, 2011 7:10 am


Emissions testing has certainly helped boost the sales of aftermarket PCMs, sensors and emission control
parts. But more importantly, it has made a significant improvement in the air quality of most large metropolitan
areas. Even so, many motorists will only seek repairs if forced to do so because their vehicle failed an emissions
test. Many put off repairs until their vehicle is barely drivable or dies and leaves them stranded.
With computerized engine control systems, it doesn't take much of a sensor input problem to adversely affect
drivability and emissions. A sluggish O2 sensor, a defective coolant sensor that always stays cold, a throttle
position sensor that has a dead spot, an airflow sensor that isn't reading accurately, etc., can all hurt
performance, fuel economy and emissions.In an attempt to ratchet up the self-diagnostic capability of PCMs, the
California Air Resources Board developed a "next generation" onboard diagnostic system called OBD II. "OBD"
is an acronym for "On Board Diagnostics." The "II" stands for "second-generation system." OBD II first appeared
in 1994, and it has been required on all cars and light trucks since 1996.
Unlike earlier onboard diagnostic systems that set a diagnostic trouble code only when a sensor failed or read
out of range, OBD II monitors most engine functions while the vehicle is being driven. It is designed to detect
almost any problem that can cause emissions to exceed the federal limit by 1.5 times.
OBD II is extremely sensitive. Some say it is overly sensitive because the vehicle manufacturers have been
overly cautious in setting trigger points below the 1.5 threshold to reduce the risk of expensive emission recalls.
As a result, some vehicles may not actually have an emissions problem when the Check Engine light is on.
Nevertheless, the problem should always be investigated to determine the cause.

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