Would love to help but I don't have my test specs handy since I'm about 1100 miles from home. may be your friend here.
And before you jump at the ECU's coolant temp sensor, make sure that the dash temp gauge and its sending unit isn't malfunctioning or otherwise broken.

 

What is your ambient temperature? Did it get really cold out recently? Seriously, gotta ask.
My truck doesnt warm for anything in cold weather, I gotta put a piece of cardboard in front of my rad. (I'm guessing my thermostat is stuck open).

 

Here are the ECT specs for an 89 3VZE. I'm 95% sure they're the same for the 22RE's sensor. I know for the 93 trucks, the two engines' ECT specs are the same. (The 93 & 89 specs a little different):
http://www.toyotanation.com/forum/sh...68#post2757478
http://personal.utulsa.edu/~nathan-b...40engineco.pdf


The only thing you need to read the codes is a paperclip to jump TE1 and E1 in the check connector, then read the flashes of the CEL. It's pretty simple, instructions are in the fsm. It's the same procedure & I think the exact same codes for your 89 as in this 93 fsm:
http://personal.utulsa.edu/~nathan-b...26diagnosi.pdf

It is NOT true that the CEL has to be on to read codes - many of the codes are stored without lighting the CEL. It IS true that your CEL has to be working - it should light up when you first turn ignition on.

 

Say what? Just jump t1 and t(e)1 in the diagnostic block and watch the CEL blink. Cost = a paperclip. LOL. Then just come on here and look up what the CEL means. Easy, breezy, beautiful... OBD1 Toyota.

 

I actually didn't know that, gonna use that next time my light flashes

 

My money says the cat issues are symptomatic as opposed to causative.