The Tire Pressure Monitoring System (TPMS) continuously check the ‘health’ of your tires, making sure they have enough air pressure to keep you safe on the road. If anything seems off, they quickly alert you on your car’s dashboard. As reliable as they are, they are prone to a wide array of problems.
For a full-size spare, the pressure should match your regular tires’ recommendation, found on the driver’s side door jamb or in your owner’s manual. The recommended pressure is usually higher due to air loss while in storage for a compact or temporary spare (a.k.a. “donut”).