Why is my tire pressure light on when my tires are fine on my Subaru?
The tire pressure light on a Subaru is usually signaling an issue with the tire pressure monitoring system (TPMS), not a visible tire defect. A sensor or relearn fault, or a temperature-related change in pressure, can trigger the warning even when the tires look fine.
Understanding what the TPMS does in a Subaru
Subaru vehicles use TPMS to monitor air pressure in each wheel. In newer models, this is typically a direct TPMS with sensors built into each wheel, reporting to the vehicle’s computer. Some older Subarus used an indirect TPMS that relies on ABS wheel-speed data to infer pressure. Either way, the system will light the warning if any tire is below the target pressure, if a sensor isn’t communicating, or if a relearn is required after wheel work.
Direct vs indirect TPMS
Direct TPMS uses individual pressure sensors inside each tire to report real-time readings. Indirect TPMS, more common on older vehicles, uses the ABS system to detect discrepancies in wheel rotation that imply underinflation. Either configuration can produce a warning even when the tire’s appearance seems normal.
Common reasons the light comes on even when tires look fine
Below is a quick overview of frequent causes you may encounter with a Subaru TPMS warning:
- A tire is actually underinflated. The system can trigger even with a 1–2 psi difference from the recommended cold pressure; temperatures can make a difference overnight or after cold starts.
- A slow leak or puncture that hasn’t visibly affected the tire’s shape yet.
- A TPMS sensor battery nearing the end of life or a failed sensor in one wheel.
- A damaged or corroded valve stem or sensor mounting, which can cause leaks or intermittent readings.
- A need to relearn the TPMS after rotating tires, mounting new wheels, or replacing sensors or tires.
- Temperature changes, especially in winter, which reduce tire pressure and can momentarily trigger the warning.
- Spare tire with a TPMS sensor (if equipped) or a miscommunication within the TPMS control module.
Other less common issues include wiring problems, a faulty TPMS control module, or a software glitch in the car’s ECU. If the light persists after addressing the obvious causes, professional diagnostics are warranted.
What to do if the light stays on
Follow these steps to diagnose and address a stubborn TPMS warning:
- Check all tires with a reliable gauge when they are cold. Compare the readings to the vehicle’s door placard or owner’s manual. If any tire is below spec, inflate to the recommended pressure and recheck after a short drive.
- Inspect each tire for visible issues such as nails, cuts, or slow leaks around the tread and especially at the valve stems.
- If all tires are at the correct pressure but the light remains, check the valve stems for damage or corrosion and consider replacing any suspect sensors or stems.
- If you recently rotated tires, had tires replaced, or changed wheels, your TPMS may require a relearn procedure. The exact method varies by model and year; consult your owner’s manual or a Subaru dealership/shop for the correct relearn steps.
- Visit a tire shop or Subaru service center if the light continues after a relearn attempt. They can scan for TPMS fault codes, test sensors, and replace a failing sensor or the TPMS control module if needed.
Note that many Subaru owners can perform a basic relearn at home, but the precise method depends on year and trim. When in doubt, a quick diagnostic at a service center will confirm whether you have a sensor fault, a leak, or a need for a relearn.
Maintaining a healthy TPMS and preventing false warnings
Proactive maintenance can reduce false or nuisance TPMS warnings and keep you safe on the road:
- Keep tires inflated to the recommended cold pressures; check at least monthly and before long trips.
- Inspect tires and sensors during routine service intervals and whenever you rotate tires or replace wheels.
- Ask about a TPMS sensor check or replacement if you notice frequent warning lights, slow leaks, or after changing tires or wheels.
- If your vehicle has indirect TPMS, ensure the ABS system is functioning correctly, as misreads can trigger false warnings.
A well-maintained TPMS helps ensure optimal tire wear, fuel efficiency, and safe handling. If you’re unsure about the status of your TPMS, a professional diagnostic is a quick, reliable step to avoid driving with improperly inflated tires.
Summary
In most cases, a tire pressure warning on a Subaru isn’t about visibly deflated tires. It points to TPMS activity—most often a truly low tire, a slow leak, a sensor fault, or a required relearn after tire work. Start by verifying all pressures with a gauge when cold, inspect for leaks, and consult your owner’s manual for the proper relearn procedure. If the light persists, have a tire and TPMS diagnostic performed by a dealer or qualified shop to determine whether a sensor, stem, or module needs service.
