Re: Autocheck code dumping confusion

[ti@amb.org (Ti Kan)]

Marc A Swanson writes:
> Ok.  Now I'm really confused.  I see that you dump codes on the mc by
> inserting a fuse on the fuel pump relay which is connected to the ECU.
> In looking over the Bentley diagrams I can't see how the ECU is connected
> to the autocheck system?!  Why does the ECU grab this "momentary" signal?
> Also, there is a "autocheck button" mentioned in the bentley.  If you
> trigger the codes with the fuse, then what does this "autocheck button"
> do?

Dumping the ECU codes has nothing to do with the auto-check system.
It dumps out stored faults in the ECU, if any.  The fuel pump relay
(and its fuse holder) is connected to the ECU and serves as a convenient
activation point.  The ECU is engine management computer and controls
such things as ignition timing, fuel mixture, turbo boost, etc.  Its
inputs are various sensors, such as ignition timing, intake manifold
pressure, intake air temperature, etc...

The auto-check is a separate system, and would light up a
pictorial symbol in the instrument cluster  if one of its monitored
devices is deemed to have a malfunction.  These devices are such
things as windshield fluid level, various light bulbs, brake and
hydraulic fluid levels and pressures, coolant temperature, etc.
As you can see, totally different things than the engine ECU.  When
you push on the auto-check "computer" button on the dash, it simply
cycles through all the pictorial symbols so that you can check that the
display is working.

Most people who transplant the turbo engine into their 4KQs forego
the auto-check system because the wiring is complex and there is no
convenient location on the dash to put the display.  However, the
code dump function is retained because the engine ECU is transplanted
intact.

-Ti
96 A4 2.8 quattro
84 5000S 2.1 turbo
80 4000 2.0
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