93 Bravada..code 81 and tranny probs

About 2 weeks ago I lost 3rd and overdrive. I checked and my tranny fluid was low and well past due for a change. So I changed the fluid and filter and that fixed the problem....until today. Today I lost 1st gear, and I think I lost overdrive. I checked the computer and it's showing a code 81. I can't find what a code 81 is. Any ideas on this one?? :banghead:

Hi Pal,
A code 81 is an antiloc brake code, Brake Switch Circuit Shorted or Open. Your code reader must pick up any code and doesen't spec whether ABS or regular diagnostic codes.
This problem tells the computer that you're applying the brakes so the computer "tells" the trans to unlock the torque converter...feels like the trans is slipping.
This switch is under the dash and is operated by the brake pedal. There's 2 switches there, one is the brake light switch, the other is the computer's brake switch we're refering to.
Are you sure the trans filter was changed? Some places do a "flush" that reverse flows fluid back through the filter? I was offered that at an oil change place which I refused and took my '92 to a regular shop that raised the back of the trans, removed the crossmember(can't remove the trans pan without it) dropped the pan, changed the filter, reinstalled the pan with a new gasket, reinstalled the crossmember then refilled the trans with about 4 qts. of fluid. Every year since I hand pump 4 qts. out through the dipstick tube and pour in 4 new qts. to improve the fluid little by little....177K on this baby.

HI Chris...I was hoping you'd reply. You helped me with my Bravada on another site last fall. Your help is greatly appreciated. I read a few posts farther down and it does look like I made a mistake. Ok- first off I'm not using a code reader...I'm just reading the blinks of the service engine soon light and getting my code. I called autozone to ask for the definition of a code 81. First..they told me there was no such thing. LOL... Then he said he pulled out a "special book" and it menttioned like 4 different things and that brake problem WAS one of them. It also said that it could be the 1-2 solenoid for your transmission. I mention that because you guys were talking about breaking off some wiring for a solenoid if you don't pull the crossmember out when pulling the tranny pan. Well guess what. Yes I'm sure the filter was changed...I did it myself. And NO...I didn't pull that crossmember...and what a pain in the butt. But...I got the pan out with a little force and some funky movements. LOL. Anyway...it kinda feels like I lost first..but I wonder if I might be misinterpreting that torque converter slipping for a loss of a gear? If I disconnect the switch do you think I'd be able to at least tell that I'm in first gear? (or would I have to bypass it?)

I see no easy fix on this one, sorry pal.
If you lost 1st right after the filter change then rechecking your work would be the best bet. If you think that the difficult reassembly might have upset the filter seal or skinned the insulation on a wire then rechecking is best...no use in possibly hurting a good $1200 transmission.