A bit of an old thread but just for others that still suffer from this issue, I would like to share how I seem to have solved the problem.
As many have described, mice indeed easily can find their way into the passenger compartment which happened to me ow that winter is coming. I have searched on fora and YouTube and below my journey to get the volvo xc90 mouse free.
1) First solution that is described is the vents in the back where the battery is located. There is a mesh in front of it however more likely to stop rats than mice and rats is not the problem. I have added wire mesh 1cmx1cm in front of it.
On the right side of the car you can do that from the inside. Note that when removing the plastic cover, the pins are likely to break but some duck tape will do nicely.
On the left side there is a lot of electronic so you can not get to it. I solved this by removing the piece of plastic in front of the bumper and removing 3 screws behind it. Just look on YouTube for the process of removing the bumper and just do the first part of it. When those 3 screws are removed, you can put in the mesh and fix it by putting the 3 screws back into place. Make sure that you have bent the mesh into the shape of the inlet however you can also shy shape it by crawling under the car and reach for it behind the the bumper.
Having thought I solved the problem with this solution, I parked the car and…… still mice.
2) so went for step 2, there is a YouTube video that shows how someone closes the outlet ports for the cowling. These are 90 degree rubber bands you can see when lying under the engine. I put in some mesh in those ports, job done.
I was not to keen on this solution since it can lead to clogged pipes which means water enters into the car, desperate measures….
Having thought I solved the problem with this solution, I parked the car and…… still mice.
Later I replaced it by putting mesh on the air intake to avoid clogging issues. In hindsight this should not be a surprise that this does not solve the problem since the intake fan blocks the path for mice.
3) this basically meant that no other documented solution was out there and I needed to find it out myself. I decided to shine a torch in the battery compartment area at night and look for light “leaking” to the outside. This showed that there indeed are more openings, in fact there are 9. You can see them when you look from the battery compartment to the bumper and you will find several round holes. Some are behind some hard foam (behind battery) so those typically are fine. The other ones however are an easy entry point into the car. Make sure not to miss the biggest hole on the left in the corner of the car (behind the corner panel) where the parking sensor enters the bumper.
I took the hot glue and put fine mesh in front of all the holes.
Having thought I solved the problem with this solution, I parked the car and…… no mice. It’s now more that 1,5 weeks where the peanutbutter cheese mousetrap is untouched so I am hopeful that this is a structural solution for this problem.
I think this is poor design from volvo and dealerships should be ashamed not doing further digging that I had to do.
Anyway, I hope others will benefit from this.