Severe strain on the brake system

The brakes will be subject to severe strain when driving in mountains or hilly areas, or when towing a trailer. Vehicle speed is usually slower, which means that the cooling of the brakes is less efficient than when driving on level roads. To reduce the strain on the brakes, shift into a lower gear and let the engine help with the braking. Do not forget that if you are towing a trailer, the brakes will be subjected to a greater than normal load.
See also:
Automatic transmission
P (Park)
Use this position when starting the engine or
parking the vehicle.
Never use P while the vehicle is in motion.
The parking brake should also be set whenever
the vehicle is parked.
...
Accessory installation
We strongly recommend that Volvo owners install only genuine, Volvo-approved
accessories, and that accessory installations be performed only by a trained
and qualified Volvo service technicia ...
Standby mode due to action by the driver
ACC is temporarily deactivated and put in standby mode:
when the brakes are applied
if the driver's seat belt is taken off
If the driver's door is opened
if the gear selector is move ...
