Check the control module

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. 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.