ABS broken, no error codes

Hello! I’m a proud owner of a 92′ 850. Unfortunately I already have problems, most of them relatively no matter, but my ABS doesn’t work anymore. When I start it, the ABS light goes off, the brake pedal makes a click. Also stays out until I brake strongly for the first time. It feels like it’s a little bit clean, but then it doesn’t do anything and the lamp lights up. I’ve already measured the sensors. One at 950, all other at 1000-1100 Ohm. The diagnostics LED (on 3 A) just lights up, the button doesn’t do anything, I don’t come any further. I’ve read that the control unit should be soldered properly, too, now doesn’t know any more…. I hope you can help here.