Just purchased this car it is a 94 LT1 auto my SES light is on so I went ahead and did a full tune up (which it really needed all plugs were loose and two wires were bad) which changed nothing light is still on. So I tried jumping the port to see exactly whats wrong and the light went out and the fan came on. Not sure where to turn now any suggestions????

 

You can't jump the port in a '94 and up. You need a scan tool or a program to read the codes. If you opt for a scan tool, get one that can do both OBDI and OBDII. Your '94 is OBDI, but chances are you'll eventually have an OBDII vehicle, if you don't already have one.

 

No, you can not retrieve the codes on a '94 and up GM by flashing the port. A scan tool or computer program is needed. The '93 model year was the last year the codes could be flashed, regardless if it's OBDI or II.

 

Also a little bit of info for ya, I had a poor running car and no ses light, I thought my on board diagnostics were screwed up or ses light was out, to find out for sure I unplugged my maf and started the car. Upon start up the light came on as well as both my cooling fans were on. I also tried to jump my obd1 port and had similar results to urs. But this is what I quickly learned, 94 obd1 cars don't give an ses for misfires, obd2 cars do, they even tell u which cylinder it is. If the problem is after the opti,(optispark) there won't be a code for misfire. Also a brief pointer, the opti in 94 cars is a spline driven non vented variety. They have a tendency to fail due to ozone and carbon retention. If it does go out, stay away from cheap parts house replacements, and u r supposed to replace the water pump @ the same time. Just some fun facts for u. The opti is the draw back to an otherwise pretty good engine imho. So my point (sorry for the long story) is that u need to either hook ur car up to a good obd1/2 scanner, preferably one that can take a snapshot of the hi and low resolution of the opti. Easiest way to tell if the opti is bad from what I've gathered, and it should also tell u if the o2's are working right or there are ways of testing the other possible problems without a scanner. Things like the MAF, MAP, IAC, TPS, coolant temp sensor, this is believe it or not a very important sensor as far as having a good running car, knock retard and other things are partially derived from the readings of this, well the list goes on, drop me a pm if u would like some info on how to start running this down. Easiest way is a scanner, but if u r like me and trapped in a town with nothing, getting ur hands on one reasonably priced is gonna be hard. Another option, go to chevy dealership. They charge 100$ or less to hook u up to a tech machine. That machine will definitely tell u what's wrong, and it's cheaper than the scanner

 

You really can't beat the free OBD-I scanning software like FreeScan (free) and DataMaster (free download, 20 free uses). Just need a cable and a laptop.

http://www.ttspowersystems.com/DataMaster.html

http://www.andywhittaker.com/ECU/Fre...0/Default.aspx

http://www.akmcables.com/

Then read this:

http://www.injuneer.com/ScanMast.html