The ALDL Connector

 ALDL Connector Diagram

To access ECM error codes: Have the engine ignition key off. For '90 - '93 cars, connect pin A to B. For '94 - '95 cars, connect pin 4 to 6. A paper clip works well as a jumper wire. Turn the ignition key on but don't start the engine. The Service Engine Soon lamp will flash with the code number. Count the blinks. The first code is always a 12. This confirms 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 displayed in numerical order, not in order of occurrence. To clear the stored codes disconnect the negative battery cable for 10 seconds.

To access CCM error codes: Have the engine ignition key off. For '90 - '93 cars, connect pin A to G. For '94 - '95 cars connect pin 4 to 12. A paper clip works well as a jumper wire. Turn the ignition key on but don't start the engine. The codes will be displayed on the speedometer display. Refer to the service manual section 8D for extensive decoding and diagnostic information.