Inspect the brake pads. If in doubt, remove the brake pads and measure the thickness of the brake pad with a vernier caliper, i.e. without the rear plate of the pad.
The wear limit of the front and rear disc brake pads is reached if the thickness of the brake pads is 2 mm.
Note: A rough estimate of the service life of front disc brake pads is 1 mm pad wear per 1000 km. This rating is given for the most unfavorable operating conditions. Under normal use, pads last much longer. With a brake pad thickness of 5 mm (without back plate) the remaining resource is at least 3000 km.
Inspect the brake caliper for brake fluid leaks. Check the piston boots for damage and cracking.
Inspect the brake discs for scratches, rust growth and cracks.