Honda FourTrax Rancher TRX420FE1 2019 Owner's Manual page 171

With the ATV on a level surface, check the fluid level.
It should be above the LOWER level mark (1). If the level is at or
below the LOWER level mark, check the brake pads for wear
(page 162).
Worn brake pads should be replaced. If the pads are not worn, have
your brake system inspected for leaks.
Other Inspections
• Make sure there are no fluid leaks.
• Check for deterioration or cracks in the hoses and fittings. If the
hoses are worn or cracked, have them replaced by your dealer.
Brakes
Servicing Your Honda 161