On Fri, 1 Mar 2013 11:21:47 -0000, "Gareth Magennis"
wrote:

The problem with cars is that they flag up error codes that are erroneous.
If you have an intake air leak, for example, the Mass Airlow Sensor gives an
incorrect reading of how much air is entering the combustion chambers, so
the fuel is adjusted accordingly and erroneously, which changes the reading
from the Oxygen sensor.
The car will tell you the Oxygen Sensor or the MAF is faulty, which people
(including mechanics in garages who often don't have a scooby what they are
doing) will replace at great expense to no effect, but still give you the
bill.

I beg to differ. Cascading errors are certainly a risk in any
monitoring system. At this time, the typical automobile just doesn't
have the CPU horsepower to include the necessary computational
resources and software needed to determine the initial cause of a
problem and distinguish it from downstream faults. I ran into this
trying design BITE (built in test equipment) for a marine radio. When
a fault would occur in an early stage, all the subsequent stages would
also show fault conditions. Since the radio was full of loops, there
was no possibility of a straight line diagnosis back to the fault
source. The 1980's solution was to attach a separate diagnostic
computer to analyze all the flashing lights. We intentionally
produced single active component failures, and recorded the light
show. That worked fairly well and largely eliminated that problem.
Unfortunately, it would not have caught a failure to turn on the
device error. The days when printers and home computahs have
self-diagnostics and error analysis built in do not seem to be in the
plan. (HP laser printer error codes are as obtuse as OBD2 codes).

Incidentally, I had a similar problem with my Subaru. The oxygen
sensor after the catalytic converter was complaining. The diagnostics
proclaimed that it was a bad catalytic converter. I read up on how it
worked and determines that the oxygen sensor was failing, which was a
much cheaper fix than a catalytic converter. If I understand how
something works, I can fix it. If I just look at the error messages
and flashing lights, I'll be like my friend and his Mercedes.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558