Diagnostic Code Error

[s10frameoff1993]

1993 S-10 pickup
2.8L V-6
5 speed

When the engine is running, sometimes the SES light comes on and is giving me ERROR CODE 12. Chilton's says something about ignition pulse references to the ECM. Can anyone explain a CODE 12 to me? What does it mean? What do I do to get rid of it? Sometimes, when the engine is running, the SES light does not come on. Any ideas on what is wrong? And how to fix it?
Thanks.

[quaddriver]

Originally Posted by s10frameoff1993

1993 S-10 pickup
2.8L V-6
5 speed

When the engine is running, sometimes the SES light comes on and is giving me ERROR CODE 12. Chilton's says something about ignition pulse references to the ECM. Can anyone explain a CODE 12 to me? What does it mean? What do I do to get rid of it? Sometimes, when the engine is running, the SES light does not come on. Any ideas on what is wrong? And how to fix it?
Thanks.

Code 12 just means the ECM is working properly, it means the key is on but there is no tach signal, which means you probly turned the key on with the ALDL diag port grounded and are counting the flashouts.

Keep counting.

1-2 will be presented 3 times as thus:

flash, pause, flash, flash, long pause repeat 2 more times.

THEN the true DTC(s) will be displayed, a '23' for example will be flash, flash, pause, flash, flash, flash, long pause, repeat 2 more times for each DTC

Then the ECM will finish up with 3 more '12' sequences.

'code readers' that simply contain an LED are a ripoff, they are a plastic housing with an A-B jumper wire and an LED between the SES port and ground - .50 cents of parts for $25

An actual code reader, like the autoxray is avail for about $250 for GM OBD1, or $350 for OBD2 and big 3 OBD1

You can get the much better Actron CP9110 for under $200 new, and the GM OBD1 catridge for about another $80, or go on ebay and score the whole lot for less (I got a cp9110, OBD2 generic, GM, ford and chry OBD1 cartridges for like $160 COMBINED off of ebay a few years back.)

If you have a big wallet, I recommend the $9000 Snapon Modis. IT does everything including brakes and includes step guide troubleshooting.

[TopDogg]

You can go to auto zone now and they read it for free.