Re: 1991 Camry 2VZ-FE Engine; CO Emission Failure


"Vince" <NoSPAM2THISHAM@xxxxxxxxx> wrote in message
news:0qse825akcraj34taur3jm4iren3io0sup@xxxxxxxxxx
On Wed, 7 Jun 2006 16:40:45 -0500, "Ray O"
<rokigawaATtristarassociatesDOTcom> wrote:


"Vince" <NoSPAM2THISHAM@xxxxxxxxx> wrote in message
news:78ge82dslvm050fa87gjbaaasb66d4c689@xxxxxxxxxx



Is there a wrap-around or some type of diagnostic test that the
dealership repair shop can perform prior to declaring the ECU faulty ?

Yes.

In the military world, a Maintenance Dependency Diagram (MDD) sounds
similiar to the repair matrix/flow chart that you mention Ray. The
MDD showed the signal path and matrix branches. The identity of all
mating connectors, relevent voltage and resistance information, and
signal waveform (o'scope) photographs are included.

The Toyota diagnostic matric sounds similar to the MDD that youa re
describing, except that there are no photographs.


When reading Jeff's previous comment, I shall mentally replace
"advanded diagnostic testing" with "additional diagnostic testing". As
with the MDDs, the fault isolation procedure was not difficult, but
needed to be performed carefully and thoroughly.


Jeff was advocating that you replace parts first and if that doesn't work,
then do "advanced" testing..

My approach is the opposite. I recommend that you check whether a
particular part is good or bad before checking it, especially when a part
like an O2 sensor can be checked in about 2 minutes. If the O2 sensor is
good, then move on to the next step in the troubleshooting chart.

The biggest reason that ECU's are erroneously replaced is that the
technician missed the "carefully and thoroughly" part.

I do not know which service department you are taking your car to, their
reputation, or whether they have MDT's. They may be very good an running
into an unusual situation or they may have dropped the ball.

Remember, I am schooled in the military electronics world. I served in
Uncle Sam's Canoe Club and was first trained as an electronics
technician for communicatins equipment. My last career had me

The individual field replaceable module could be either self-tested or
bench tested by shipboard technicians. OTOH, a magnetron was replaced
after other possible causes of poor radar video returns were
tested/evaluated. It is good to know that the auto repair industry
also has been designed to avoid needless replacement of field
replaceable modules.

Even in the days when equipment used vacuum tubes, the electronics
technician would test the tube in a tube checker prior to replacing
it. So, I was taught to "fault isolate" down to replaceable
component, e.g., tube, PC board assembly, rather than replace a tube
or PCB assy and hope for a "fix". Signal flow diagrams included
waveform photos as required, and those were referenced to within the
MDDs, rather than the MDD itself including a (timing) waveform, etc.
Sure, in some cases there remained more than one possible field
replaceable module that could possibly cause a symptom. This is where
I had to consult the electrical design engineer and possibly the
reliability engineer to possibly provide a "most likely" list of the
candidates.

It sounds like there is little difference in the diagnosis and repair of
shipboard and automotive electronic systems.
--

Ray O
(correct punctuation to reply)


.

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