Check the control module

WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Control Module

Courtesy of VOLVO CARS OF NORTH AMERICA.

Check:

that the control module is of the correct type (this depends on whether the car is equipped with STC or not)
that none of the pins or sockets on the connector are damaged
that there are no contaminants on the mating surfaces between the control module and the ABS hydraulic modulator
that no part of the control module seals remain on the ABS hydraulic modulator valves.