1994 850 T5 Wagon Auto Trans Issue

[Bricked850]

As the title states, I'm having issues with my transmission.
I started my car and started driving, but my transmission was slipping. After checking the level, I added a quart of ATF and a bit of Lucas Stop slip, and it seems to be back to normal, but it does occasionally slip in 1st.
I also have the up arrow flashing (which I am aware is a transmission fault).
I'm curious about how to diagnose the light and possibly reset the computer (I tried to reset it by disconnecting the battery for a few hours, to no avail). Do I need to buy an OBD1 scanner or will the paperclip method work as well?

[Swedespeed96]

Have you tried disconnecting both terminals and touching them together for 30 seconds

[TheVolvoNut]

Your built in obd-1 system should give you a code to point you in the right direction. A1 is for the transmission, as well as A5, which covers the transmission control unit.

[05V70RGT]

I believe only 95 had the built in code reader but I could be wrong. Its been known to happen.

[tardcart]

a flaw in the 850 is the limp mode for the transmission. It goes into 3rd gear which will burn the plates up if driven. Never drive with the blinking arrow. in almost every case its the pnp switch not knowing what gear its in, this is a cold weather problem when the grease get hard in the switch. You must clear the code. Its best to start the car in neutral if having this problem, let it warm up then shif to drive. at least you have skipped over park and reverse . the repair is hard. its under the battery and air box. the switch can be disassembled and cleaned and new dialectic silicone grease applied, then put it back exactly where it was as told by corrosion around the hold down bolt. if using a new one, use only Volvo.
some line it up viewing the reverse lights in a mirror when the shift is in reverse.

[Bricked850]

Your built in obd-1 system should give you a code to point you in the right direction. A1 is for the transmission, as well as A5, which covers the transmission control unit.

The code is 313, which I'm going to look into once it warms up a bit. I'm told it's a pretty generic code, but I've had the battery disconnected for a few weeks now, so maybe it self healed (I've been pretty lucky like that) but I'm going to follow the other tips too, thanks guys!