First, verify that it's OBD-I and not OBD-II.  You should be able to do
a web search for the OBD-I protocol spec, but not sure if that would be
published for OBD-II.  Output should be codes (not sure of format) with
a "standard" format -- ie:  for OBD-II, the first char is the problem area
(P=Powertrain, C=Chassis, B=Body, U=Network), the 1st digit is the
mfgr or SAE, etc.  The next digit is a more specific area -- ignition, fuel
metering, emissions, etc, and the last couple are the actual trouble code.
The tool may have a lookup table with the text messages, or you could
look them up manually.  I'm sure OBD-I is different though, but you get
the idea.  The actual protocol I'm unaware of.

If you are doing this to develop a commercial product or really want
to use a PIC, then may the force be with you.  Otherwise it may be
better to borrow one, pick it up used, or run by a local Autozone,
PepBoys, etc and use theirs for a few bucks.  Recently had a problem
with my Audi, and it uses a VagCom -- an OBD-II with some Audi
extensions.  Very expensive device, but I found a web site that lists
VagCom owners around the US that will let you borrow for free or
a beer, etc.

Hope it helps,
-Neil.



----- Original Message -----
From: "Herbert Graf" <hgraf@EMAIL.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, February 26, 2002 10:18 AM
Subject: [EE]: OBDI tools?


> 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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