Locate the OBD spec before you invest time in building a device for this.
I don't think that OBD-I can tell you at what points the car is in closed
loop or not.  Even if the check-engine light does not go on, the jumper
test will flash the appropriate trouble codes for any sensors that it
detects are out of spec.

Since it's free and basically one wire, I highly recommend this route before
investing time and money into building a "blind" device.

Cheers,
-Neil.


----- Original Message -----
From: "Herbert Graf" <hgraf@EMAIL.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, February 26, 2002 2:25 PM
Subject: Re: [EE]: Re: OBDI tools?


> Hello, thanks for the info. We've used this trick many times in the past
and
> it has been very helpful, however we now need some more "internal"
> information to figure something out. First we need to know whether the car
> is coming out of closed loop, and if so what sensor is slightly out of
spec
> causing closed loop to be lost. It's the kind of thing that doesn't cause
a
> check engine light, since the car still works pretty much fine, it's just
> that our in-city mileage has gone up quite a bit, and if we don't figure
it
> out we may need to get a new catalytic convertor before the next emission
> test. Thanks, TTYL
>
> > -----Original Message-----
> > From: James Paul [mailto:jamesp@intertex.net]
> > Sent: Tuesday, February 26, 2002 00:49
> > To: PICLIST@MITVMA.MIT.EDU
> > Cc: hgraf@EMAIL.COM
> > Subject: [EE]: Re: OBDI tools?
> >
> >
> >
> >  Herbert,
> >
> >  On GM cars, reading the codes is easy.   Under the dash usually close
to
> >  the steering column is a connector with 12 or so positions in it.
> >  They are marked with letters.  Using a short piece of wire, connect
> >  terminal "S" to terminal "A".  Turn on the key, but do not start.
> >  The codes will flash out on the "Check Engine" or "Service Engine Soon"
> >  lamp in the instrument cluster.   As far as decoding what the codes
mean,
> >  I could probably tell you later on today when I get home.  Otherwise,
you
> >  could go to the library and get a service manual for your vehicle or
you
> >  possibly could talk to a mechanic and have him decode them for you.
> >  But anyway, that's how you can read the codes on GM vehicles.
> > If you have
> >  any other questions, let me know after about 6:00 PM tonight, and I'll
> >  see what I can dig up at home for you.
> >
> >  Hope this helps you out.
> >
> >
> >                                                   Regards,
> >
> >                                                     Jim
> >
> >
> > > Have an '87 Buick Park Avenue we'd like to diagnos a problem on. It
> > > would really be helpful if we had a "scan tool", however they are
> > > stupidly expensive. I've done some searches and it looks like the data
> > > that comes out of the ECM is simplly serial data at 8192bps at 12V
> > > voltage levels. Does anybody have more info on this? Is the output
text
> > > or is it just a bunch of hex digits? If so anybody have a mapping for
> > > which hex digits mean what? For now I'll be using a PC laptop but it
> > > sounds like this might be something I can build with a PIC if I can
> > > find this info. Thanks for any help. TTYL
> > >
> > > --
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> >
> >
>
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>

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