1999 SAAB 9-5

The wheel speed from the wheel speed sensors is an input to the TC/ABS module. From there, it is put on the bus to the main instrument unit(cluster), and the trionic module(engine control module). The abs lights are on correspondingly. The left rear sensor is the one responsible for vehicle speed. The AC voltage, from that sensor would need to be checked at the sensor, as well as resistance of the sensor.

U need to read abs unit codes, too for better repair directions, those codes start with letter C, but anyways u may have a bad abs unit, get further codes checked using a tech2 scan tool, with saab software installed, good luck.