I pasted the information below from the "sticky" on this Forum.
THE ALDL CONNECTOR:
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[FONT=Courier New, Courier, mono]| F E D C B A |[/FONT]
[FONT=Courier New, Courier, mono]| M L K J I H |[/FONT]
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To Display Trouble Codes:
Run a wire or paper clip from Pin A to Pin B then turn the ignition on but do not start engine. The "Check Engine " light will flash in the following sequence: flash, pause, flash-flash, long pause flash, pause, flash-flash, long pause flash, pause, flash-flash, long pause. This is a code "12" which will always be there and tells that the diagnostic test is working. After this series of flashes and pauses any stored trouble codes will now flash. If you do not see the "12" flash three times, your diagnostic circuit is defective.
Most vehicles will display stored trouble codes, then "12" again.
If you short pin A to pin B; then re-start a fully warmed up engine, you can set the timing to 4 degrees BTDC. Then shut off the engine and remove the short between pin A to pin B. The check engine light will be on with pin A to pin B shorted.
After the timing is set you can check to see if the ECM is getting into closed loop. Re-starting a fully warmed up engine with pin A to pin B shorted the check engine light will flash. If the check engine light is flashing at a rate of about 2 flashes a second, the engine is in open loop. If the check engine light is flashing at a rate of about 1 flash a second, the engine is in closed loop.
dave w