Here are the destructions straight from G.M.
1. Turn ignition off
2. Ground ALDL Terminal K (this is the lower row, 3rd from the right).
3. Turn ignition on
4. Wait for fault codes to begin flashing (approx 5 seconds). When the codes begin flashing, unground ALDL terminal K for 3 seconds + or - 1/2 second.
5. After ungrounding ALDL K as described in step 3 above, ground it again for 3 seconds + or - 1/2 second.
6. Unground ALDL K and wait 10 seconds. Before turning the ignition OFF, verify that code 12 is the only code being flased (this is the seatbelt/air bag light flashing). If not, codes have not been properly cleared. Repeat from step one if codes not cleared until the codes clear.
When I do this, I put a jumper wire on K and used some aligator clips to ground it to the driver door hing (cuz I have the door open the whole time). You can ground, unground th aligator clip to the jumper to clear the code.
See, I saved you some money!