Accessing GM Serial Data (was: Help needed reading Ford

[Donald Whisnant]

At 11:10 AM 11/26/95 EST, you wrote:
>My 1984 Riviera has a 12-pin ALCL connector under the steering column.  I
>have a GM service manual for a 1983 Grand Prix which says the pinout of this
>connector is as follows:
>        A       Ground
>        B       Test Terminal
>        C       Air Select/Early Fuel Evaporation Solenoid
>        D       "Check Engine" Light
>        E       Unused (no wire)       
>        F       Torque Converter Clutch Solenoid
>        G-L     Unused (no wires)
>
>The connector in my car seems to match this description.
>
>Grounding the "Test Terminal" with the engine not running will cause the
>system to display the trouble codes on the "Check Engine" light, activate
>all the solenoids and motors under the hood, and the ECM will not record any
>additional codes while troubleshooting.  Grounding the "Test Terminal" with
>the engine running causes the system to display the codes on the "Check
>Engine" light and prevents the sysetm from storing any new codes.  The
>manual also says to set up the TPS for example, a digital voltmeter must be
>"tapped" into the leads at the sensor.
>
>I got hold of a Mitchell maunal for the car which says pin E of the ADCL
>(which comes from pin 8 of the ECM) is for serial data, but there is
>physically no wire on this pin in my car!  My Grand Prix manual says pin 8
>of the ECM is the Throttle Control Switch Input.
>
>I took my car to a mechanic friend of mine and mentined that I was having
>troublegettin my TPS adjusted properly, he took out his Scan Tool, plugged
>it into my ADCL and was able to read the TPS voltage on the display.
>
>One of the readers sent me some interesting information of the GM serial
>data communications protocol which seems to run at 160 baud and says that it
>is a continuous data stream. Another reader has explained the format of the
>data, but my remaining question is WHAT PIN IS THE DATA ON AND/OR HOW DO YOU
>GET ACCESS TO IT?
>
>Lloyd Ferguson
>ferguson at srcing.login.qc.ca
>

How about pin M?  Do you have a wire on it?

                   -------------------------
                   | F | E | D | C | B | A |
                   -------------------------
                   | G | H | J | K | L | M |
                   -------------------------

  (most are as you've listed above)

      A - Ground
      B - Diagnostics ("Test") terminal
      C - Air Select/EFE
      D - MIL ("Check Engine Light")
      E - Serial Data (on older ECM's)
      F - TCC (Torque Converter Clutch)
      G - Fuel Pump
      H - Brake
      J - ???
      K - ???
      L - ???
      M - Serial Data (on newer ECMs/PCMs)

The newer ecms/pcms (at least 93 vehicles) have a serial data wire on pin M...

Donald Whisnant
dewhisna at ix.netcom.com