Accessing GM Serial Data (was: Help needed reading Ford
Donald Whisnant
dewhisna at ix.netcom.com
Sun Nov 26 21:12:17 GMT 1995
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
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