The '90 - '93 ALDL Connector

 

          

To access ECM error codes: Engine ignition key off. Connect pin B to A. Turn the ignition key on but don't start the engine. The Check Engine lamp will flash with the code number. Count the blinks. The first code is always a 12 to confirm that the diagnostic system is working. Count one blink with a short delay and then two blinks for a 12. The 12 code will flash three times. The next code is the first error code. It will also flash three times. Record all of the codes until the 12 is flashed again. That means that all of the codes have been flashed and that the system has looped to the beginning of the list. The codes will be listed in numerical order.

To access CCM error codes: Engine ignition key off. Connect pin G to A. Turn the ignition key on but don't start the engine.