If your vehicle is showing hissing sound coming from the tire or valve stem, here are the most likely causes and the parts you'll need to fix each one.
A nail, screw, or other sharp debris has pierced the tire tread or sidewall, allowing air to escape rapidly enough to create an audible hiss.
The small internal mechanism (valve core) inside the stem is loose, contaminated with dirt, or has a failing seal, causing a steady leak from the tip.
The rubber body of the valve stem has cracked due to age, UV exposure, or physical damage, causing air to leak from the base where it meets the wheel.
The rubber grommet or retaining nut securing the TPMS sensor to the wheel is corroded, over-tightened, or was improperly seated during a recent tire installation.
Corrosion or dirt build-up on the wheel rim prevents the tire bead from sealing completely. This often occurs if the rim wasn't properly cleaned during a recent tire mounting.
A severe impact with a pothole or curb has caused a hairline fracture in the metal wheel itself, allowing air to escape through the crack.