Kyle......I got the P0125
on my '96 a month ago. My coolant level was a bit low.....topped it off, cleared the code and no worries since.
Otherwise, it may be your PROM (seeing as you have a '96).......there is an update PROM to take care of erroneous P0125 codes, but it's wasn't a recall so ya have to pay for it. On the upside it is something you can do yourself.
Check the coolant level 1st of course
is referring to your downstream (past the cats) O2s and is telling you that something is up with the heater circuit. Your O2s have a built in heater to get them up to temp quickly during start-up and keep them there during idle. One of two things is happening: the heater is dead or the electrical connection is open. If the heater is dead you need to replace the O2. Check for open circuit 1st though. Power for the heaters come via fuse F3 in you fuse panel - check it. Disconnect the 4-wire connectors to the O2s and clean them w/ electrical contact cleaner, give them a few minutes to insure they are dry and then plug 'em back in.