Speed steering sensitive relay
 

After years of hard steering I replaced the steering pump on our 07 xc90. Since doing so on the motorway the steering is pretty light, I had a gander and found a relay plug under the steering / above brake pedal and done a search on that.
There isn't a relay on there what relay should be?

depends on if you have that option installed from factory

Whilst the connector has the form factor of a relay base, the unit isn't a simple relay. Volvo refer to it as the "Servotronic module" and it's actually a digitally controlled current source, which directly drives the fluid bypass value on a speed sensitive rack based on signals from the CAN bus. The drive is proportional to road speed, not all-or-nothing.

That said, it was an option on most models so there's no guarantee that yours is "missing", it may never have been fitted. I don't know without looking but if you have access to VIDA, I'd be surprised if this option wasn't listed in the car's configuration data along with the factory-fitted status (i.e. originally fitted, or not).

Failing that, you could give a local dealer your chassis number and ask them for the part number for the module. They should be able to tell whether your vehicle was actually supplied with one, and if so, even if you don't go on purchase a brand new module from them, the part number is still useful - these turn up on ebay a lot but to guarantee plug-and-play compatibility with your particular vehicle you need to fit exactly the same part number (there are many variants).

And even failing that, you could always try the one from your V8, which would have that option fitted as standard. It's not going to cause any harm if your D5 doesn't actually have the software and/or speed sensitive rack option fitted.