If your vehicle is showing tire loses air pressure slowly over a few days or weeks, here are the most likely causes and the parts you'll need to fix each one.
A small nail, screw, or piece of debris has punctured the tire tread, creating a tiny hole that allows air to escape very slowly over time.
The rubber valve stem has dry-rotted, or the sealing grommet on the TPMS sensor has degraded, allowing air to leak directly from the valve area.
Corrosion, rust, or peeling clear coat on the inside lip of the wheel prevents the tire bead from forming a perfect airtight seal against the rim.
During a recent tire installation, the technician failed to wire-brush the wheel bead clean or pinched the TPMS sealing O-ring, causing a slow leak.
A severe impact with a pothole or curb has bent the lip of the rim or caused a hairline crack in the barrel of the wheel, breaking the airtight seal.