Where to plug in the code reader on a 1994 T-100

Likely a transmission code the reader cant see. Suggest you try a better $$$ reader.

Are you asking how to clear the check engine light?
Buy a cheap code reader ( $20 ) plug it in the OBD2 port which has to be no more than 3 feet from the steering column and clear the code(s).
If the check engine light comes right back on after you have cleared the code(s),read the code(s) and correct the problem(s).

year vehicle manufactured? if 1996 & later, OBDII scanner to be plugged into a port (typically, should be near the steering column, under the dash).
older models may have OBDI (no standard location of port) scanner specific to the make of the vehicle. search the web, on how to read manually (or without scanner) the code by counting the number of blinks of the MIL (malfunction Indicator light) (aka check engine, or service engine soon).




Autel MaxiScan MS309 OBD II Code Reader Scan Tool

It should be right above the pedals, under the dash. Use a flashlight and you should see it.

This is not possible without an error code reader Unless you have check engine or service engine light Then you can hotwire the port for connecting scanner
and it will flash the code to you using the check engine light on dash
But its quicker to use a reader.
Different car models you can get to flash codes to you contact you car dealer to enquire about it.

I have this model Saturn (2003 LW300), and bought a code reader off Ebay. Make sure it is a compatible "OBD2" type, and plug is seated firmly with ignition switch off. Then turn on ignition without starting car. Press "Enter" or something on reader to start it and it should work.

You can go to any auto parts store, ask to barrow an OBD-II Code reader. Plug it into your cars computer data port (Usually on the dashboard, on the drivers side, close to the lower portion of the dash) and push erase.
However, you should find out what the computer is telling you first, and/or fix the problem. Engine service lights, run on a circuit that only completes itself once every 20-30 times you start your car. This means, if you were to just erase the engine code, the light will go off, but will just turn back on eventually.

NO CODES TO SHOW?

The engine light could be on for an unrelated reason. Most major auto parts stores will scan and clear codes for free or have a loaner you can use on site. The reader plugs into a port under the dash on the drivers' side....get the code number, then clear it with the reader. If the same code comes back, post it here or Google it for additional help

You could have a restriction in the egr ports. remove the valve. Plug the holes, start engine. 1 hole will be blowing out exhaust, the other will have large vacuum.