GM diagnostic harness

[Joe Healey]

I have an 87 Chevy Cavilier and am interested in building a circuit
that can capture, decode, and display ( in some fashion ) the data
comming out of the car's diagnostic harness.

Does anyone know of where I can find a technical specification
describing the dignostic interface and data stream or if a circuit
allready exists ( ie Radio Electronics ) to do this.

I know that these scan tools can be bought, but they are too
expensive for me to purchase.

Since I cannot post directy please respond to me at the following
address. Many thanks in advance.

Joe Greco
jgr...@ll.mit.edu

[Randy Agee]

I read Joe's request for info with extreme interest. I also
have a GM car with an ECM. I know from service manuals and
experience that I can get the "hard" fault codes out of the
computer by placing a jumper over two terminals and reading the
flashes on the Service Engine Soon Light. I also know that
with the proper SCAN tool that all the sensors can be polled and
the various voltage levels that control the spark advance, fuel
injection, etc. can be be monitored. I am extremely interested
in pursuing the analysis of this data. I see no reason why a
portable PC with the proper connector and software could not
analyse the data stream through the RS-232 port, for example.
Is there something already out there? Does any one have info
or know where to find it to develop the software? Responses
here or by E-Mail would be greatly appreciated. My local GM
folks just look at me like I am crazy when I ask about
documentation on the data stream.

ra...@vdoe386.vak12ed.edu
Randy T. Agee (ARS WB4BZX)
--
================================
Randy T. Agee
Virginia Department of Education
Richmond, VA

[Ken Mosher]

There is product called
"Diacom" that uses a laptop PC to display the data dumped at one
second intervals from the ECM. The reports generated are quite comprehensive.
The cost is around $250-300 for the software and cable. I have received a
demo version of this software recently and I am impressed. I'm considering
ordering it, but it would be a lot more fun to write my own program!

Several of us who race Buick GNs find either the Diacom or OTC Scan tools
invaluable in tuning. I personally use the OTC.

-- Ken Mosher
-- Buick Grand National: A *BOOST* of Buick Performance!
--
Ken Mosher UUCP: uunet!sparky!kmosher =
Sterling Software IMD INTERNET: kmo...@sparky.IMD.Sterling.COM =
Buick Grand National: The Surgeon General never said anything about smoking =
the competition!! =

[Willie Peloquin]

In article <1992Sep24.1...@ll.mit.edu> j...@ll.mit.edu (Joe Healey) writes:
>
>
>I have an 87 Chevy Cavilier and am interested in building a circuit
>that can capture, decode, and display ( in some fashion ) the data
>comming out of the car's diagnostic harness.
>
>Does anyone know of where I can find a technical specification
>describing the dignostic interface and data stream or if a circuit
>allready exists ( ie Radio Electronics ) to do this.
>
>I know that these scan tools can be bought, but they are too
>expensive for me to purchase.

I just saw a ECM diagnostic tool at a local discount auto parts store. The
cost was @ $40.00. There were three models available. One for each American
car manufacturer.

So they are available and they are fairly inexpensive!

Willie
--
Willie Peloquin | I'm not a kid anymore, but this ain't no
wpel...@medar.com | midlife crisis, because whiskey and women
uunet!medar!n8mdy!wpeloqui | have always been my vices! Bocephus

[Mark Shaw]

In article <Bvrpp...@medar.com>, wpel...@medar.com (Willie Peloquin) writes:
|> In article <1992Sep24.1...@ll.mit.edu> j...@ll.mit.edu (Joe Healey) writes:
|> >
|> >
|> >I have an 87 Chevy Cavilier and am interested in building a circuit
|> >that can capture, decode, and display ( in some fashion ) the data
|> >comming out of the car's diagnostic harness.
|> >
|> >Does anyone know of where I can find a technical specification
|> >describing the dignostic interface and data stream or if a circuit
|> >allready exists ( ie Radio Electronics ) to do this.
|> >
|> >I know that these scan tools can be bought, but they are too
|> >expensive for me to purchase.
|>
|> I just saw a ECM diagnostic tool at a local discount auto parts store. The
|> cost was @ $40.00. There were three models available. One for each American
|> car manufacturer.
|>
|> So they are available and they are fairly inexpensive!

Those "inexpensive" ECM diagnostic tools in the auto parts store are
nothing more than an overpriced jumper wire with booklet full of
failure codes. You can do the same thing with a piece of wire and
the factory (Helm) shop manual. On my GM cars I just short the
two appropriate pins together and the "CHECK ENGINE" light flashes
the error code number.

Mark

[michael dale townsend]

ma...@wdcwdc.sps.mot.com (Mark Shaw) writes:
>. . . . . You can do the same thing with a piece of wire and

>the factory (Helm) shop manual. On my GM cars I just short the
>two appropriate pins together and the "CHECK ENGINE" light flashes
>the error code number.

>Mark

Do the shop manuals tell which pins are the "appropriate" pins?
Also, my 1977 Pontiac Grand Safari has a couple of suspicious looking
wire harnesses under the hood. (One is near the air-conditioner btw.)
I didn't know that they had the diagnostic computers in cars back then.
Does anyone have any info or ways to get info on this? I'd like to
capitalize on this if possible.
Michael Townsend mic...@hubcap.clemson.edu