[V]

Trouble code retrieval
With the engine not running, key in the "on" position, jumper terminals "A' and "B". With the ecm in the diagnostic mode, it will first flash a code 12, indicating the ecm has entered this mode. You will see the SES do this for a code 12: flash, pause, flash, flash. Think of it in on/off state: 1, pause, 1+1 = 1+2, or 12. It will flash this code three times, then there will be a short pause, and it will flash code 12 again three times, as long as there are no trouble codes, the ecm will flash this over and over until the jumper is removed from the ALDL.
If there are trouble codes stored, it will follow the code 12, starting with the least numerical code first, flash it three times, go to the next numerical code, flash it three times, and so on until it has reached the last code. Then it will flash code 12 again, and start the whole process again, until the jumper is removed. This will give you plenty of time to retrieve the codes, and double check yourself to make sure you have written down the right ones. Example: Code 34: flash, flash, flash, pause, flash, flash, flash, flash. (1+1+1, pause, 1+1+1+1= 3+4, or 34.
Below is a list of trouble codes:
12 ecm diagnostic mode
36 maf burn-off malfunction
13 oxygen sensor
41 ecm tach signal failure
14 cst voltage low
42 est failure
15 cst voltage high
43 esc (knock sensor)
21 tps voltage high
44 lean exhaust
22 tps voltage low
45 rich exhaust
23 mat voltage high
51 prom failure or installation
24 vss
52 calpak missing
25 mat voltage low
53 high battery voltage
32 egr system malfunction
54 low fuel pump voltage
33 maf or map reading high
55 defective ecm
34 maf or map reading low
61 Oxygen sensor
35 idle speed error