I have a '97 formula and just recently my abs inop light came on while I was driving. It wasn't until today that I fell restriction while trying to give it gas. When I'm braking I can feel shaking coming from the rear of the car like it could be a bad rotor but I'm not sure if that is the problem. The car has 160k on it, and it has the original calipers on it. Checked the brake fluid, and it was filled to the top. Don't want to take it into a mechanic to get the code read unless I absolutely have to.

I didn't know if a bad caliper, rotor, or both could cause that light to come on in the dash. If it's not those items what else can it be?

Sounds to me like a bad caliper or a bad brake line going to the caliper.. Heres how you can check to see if its the line.

Jack up the rear of the car and put it on jack stands. have someone sit in the car and pump the brakes a few times and hold on the brake. Crack open the bleeder valve on the back of the caliper and if no fluid comes out then its most likely the line thats going into the back of the caliper thats gone bad. If fluid does come out, the brake pedal should slowly go to the floor. When the brake pedal is compressed all the way to the floor, close the bleeder valve. Make sure that the brake pedal is not let up on or you will be sucking air back into the caliper and into your brake line system which is a BIG NO NO.

If you do get fluid coming out of the bleeder then its not the line and its the caliper.
If you dont get fluid out of the bleeder valve then its the brake line going into the caliper and NOT the caliper itself.
If both of those are ok then you will most likely need to swing by a garage and have them take a look at your ABS system and see where the fault is.

Usually rotors dont go bad unless you havent been changing your brakes regularly and wearing your pads all the way down to the metal and eating into your rotor. Ive seen rotors that are thin as paper and it amazes me how some people are actually stopping. Hell Ive even seen some thats gone past the rotor and its actually hitting the ribs on the INSIDE, the ribs that are holding the 2 sides of the rotor together.

Also could always swing by Advance Auto in your town and have them scan it for free and get the code from them.

Very first thing i would do would be to clean off the little ABS sensors inside the wheel. You can only get to them from the inside of the rim (it's the only wire there). Check those because sometimes they get dirt and other gunk on them, causing them to misread and think that your car has lost traction, causing the brakes to pulsate. Sounds like that's the problem. Just wipe them off and plug em back in...should take no more than a few minutes. Then take it for a spin, i'm pretty sure your problem will be fixed

I had the exact same problem, and went through all the things suggested, cleaned the sensor, checked the rotors, everything I could think of. Then I replaced the shocks, never happened again. They seemed to be ok, passed the bounce test. They were just bad enough to give the car a tiny bit of wheel hop in the back which was triggering the ABS inop light. If the car haddn't bottomed out when I had it heavily loaded in the rear (two passeneger in back, cooler and various other load objects) I would never have gone down that road. Take two of your weight challenged friends for a ride and see what happens

I would also change the brake fluid and bleed all 4 corners with new fluid.

Matt