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From: rls@iham1.UUCP (Rick Schieve)
Newsgroups: net.auto
Subject: Re: Idiot light question.
Message-ID: <181@iham1.UUCP>
Date: Fri, 10-Aug-84 09:31:52 EDT
Article-I.D.: iham1.181
Posted: Fri Aug 10 09:31:52 1984
Date-Received: Sat, 11-Aug-84 00:27:32 EDT
Organization: AT&T Bell Labs, Naperville, IL
Lines: 25

The check engine light on late model GM cars does not really
qualify is an idiot light as most people think of them.  It
does not monitor a specific engine function, but rather it
lets the driver know that the computer control thinks something
is wrong.  The computer has multiple inputs such as engine temp,
barometric pressure and even a sensor in the exhaust.  It in
turn controls gas flow, spark advance, etc...  Any time the
check engine light comes on while driving, it is an indication
that the computer is not happy with something and if it is not
happy ist can screw up the car in many ways.  The fact that the
light came on tells no specifics.  THowever, as long as power is
not lost to the computer, it remembers what it was complaining
about.  Its memory can be dumped by shorting two terminals
together at the diagnostic jack under your dash.  The check
engine light will actually flash an error code indicating its
specific problem.

Buy or borrow a service manual.  The specific procedure along
with diagnostic flow charts will probably pin point your problem.
I was skepticle myself until my wife's 81 Camaro had some problems
and after reading the error code the service manual pointed right
to the faulty computer temperature sensor (which is not the same
as the sensor that runs gauges or idiot lights).

				Rick Schieve