SES light flashing while driving, high idle, can't read dtc codes. Limp mode?

[BoominSVX]

Howdy fellas, I could use a hand here. Dad's 92 Sierra 2500 got a little silly after a weekend long nap. He took it to work this morning noticing that it was idling very high on start up (Even higher than the usual abnormally high fast idle) and it began flashing the CEL somewhere on the trip and running like poo. Probably a misfire. I can figure this type of stuff out eventually with time, but it all starts with scanning for codes and I CAN'T DO IT. That's the trouble. The paper clip idea didn't work at work, the wire didn't help, and my obd1 wal-mart (fancy bigger paper clip) scanner is no different. I can't get her to scan. I pulled the computer and checked the connections, reseated the chip, checked the wires, and seem to have ground on terminal A and a few volts (dull test light) on terminal B. I checked both ign and ecm fuses... they look good. I got 12 volts at the orange wires and 12 volts switched on the pink as well as a few others. The ground looks good on the thermostat housing. Nothing smells burnt. Only thing I see that is questionable is the brown/white that supposedly has to do with the DLC is putting out a switched 12 volts with the computer unplugged. I'm not sure if it's supposed to do this. Continuity testing shows 5 other wires also have some form of connection to this wire on the same plug at the ECM, but I doubt it could melt that many wires together. It does have a slight bubbling to it though. I attribute that to an idiot playing with computers over a distributor issue. So what do you guys think? Bad ECM? Is there any way I can try the jumper wire right at the computer if I remove the pin to the DLC... just to be sure that computer has actually $hit out? I'll test for days before I start throwing money at random parts.... especially hard to find ones like a 1992 ECM. I could use a little confirmation. Please reply if you have any relevant ideas or experiences. If you read this far, I appreciate it already.

 

[BoominSVX]

Ok guys. I got it covered. I checked alldata and found a few diag helpers and some info on pin location. I have a 4l80e in this truck, so yours may be different, but the process should be the same. Pull the 24 and 32 pin connectors out of your ecm or pcm (however you know the computer to be named) and turn the key to ON. If the SES light is still on then you have a short somewhere and it's not grounding the diagnostic pin. Trace the wire and fix the issue. If the light is now OFF (like mine) then plug it back in. Take a test light and ground it to the body with the clip, then tap/probe the white/black stripe wire. On my PCM it was on the 32 pin connector a C or D 6. Can't remember which side. This is a direct connection to the diag port. No wires to cross. If the Service engine soon light is still on when you turn the key to ON and won't flash you a code 12 at this point, the pcm is bad. I got one at Advanced Auto for 73.99. It won't come with a PROM, so keep yours as well as the lid. This fixed mine, but if that failed as well, the last step would be to replace the PROM. All is well and she's running better than she has in a long time. I found a vacuum leak so a quick rebuild of the throttle body may have helped that a bit. Maybe I'll put his brake light bulb back in and see if that was part of this slow death.

Oh, it died from sitting in the sun and 90 degree heat over the weekend. That's all it took. Just FYI. It won't really be a slow process from what I've read. Hope this helps somebody someday.