Heating the crimping sleeve
WARNING: This page is about a different car, the 2004 Volvo S40, 2003 Volvo S40, 2002 Volvo S40, 2001 Volvo S40, and 2000 Volvo S40. However, it is still accessible from the selected car via links, so may be relevant.
Hold a putty knife or other suitable protection behind the heat-shrink tubing to shield the surrounding components from heat.
Heat the sleeve with hot air gun: 9512777 and a suitable nozzle. It is important that the heat-shrink tubing is shrunk around the cable. It should be possible to see some adhesive that has squeezed out around the cable.