What Is TPMS?
TPMS stands for Tyre Pressure Monitoring System. It is an electronic system that monitors air pressure in your tyres and warns you — via a dashboard warning light — when one or more tyres are significantly underinflated.
TPMS is fitted as standard on most cars manufactured after 2012 and is increasingly common on NZ new-car market imports. Its purpose is simple: underinflated tyres increase the risk of blowouts, reduce wet-weather grip, and degrade fuel economy. TPMS gives you an early warning before pressure drops to a dangerous level.
The TPMS warning light looks like a cross-section of a tyre with an exclamation mark inside (!).
How Does TPMS Work?
There are two types of TPMS:
Direct TPMS
Each wheel has a pressure sensor and transmitter mounted inside the tyre (attached to the valve stem or banded to the wheel). These sensors measure actual air pressure and transmit data wirelessly to the TPMS control module. Direct TPMS is the most accurate system and tells you the exact pressure in each tyre.
Indirect TPMS
This system uses the existing wheel speed sensors (part of the ABS system) to detect when a tyre is underinflated. An underinflated tyre has a smaller diameter and rotates slightly faster than correctly inflated tyres. The system detects this speed difference and triggers the warning. Indirect TPMS is less precise — it cannot tell you which tyre is low or by how much.
Most modern NZ-market cars use direct TPMS, including common grey imports from Japan that were originally sold for the Japanese domestic market.
What Triggers the TPMS Light?
The light typically illuminates when one or more tyres are 25% below the recommended pressure. For a tyre with a recommended pressure of 220 kPa, the light would come on at approximately 165 kPa.
Common triggers:
- Temperature drop — tyre pressure decreases roughly 1 kPa for every 5°C drop in temperature. A cold South Island morning can trigger the light in tyres that were fine in warmer weather
- Slow puncture — a nail or screw causing a gradual leak
- Natural air diffusion — all tyres lose 1–2 kPa per month normally; eventually pressure drops enough to trigger the light
- Fitting new tyres without resetting the system — can cause false readings
- Dead sensor battery — direct TPMS sensors run on internal batteries lasting 5–10 years
What the Flashing TPMS Light Means
- Steady light — one or more tyres is underinflated; check and inflate all four tyres
- Flashing light (for 60–90 seconds then stays on) — a TPMS sensor fault; the system itself has a problem and needs diagnosis
Resetting TPMS After Inflating Tyres
For direct TPMS systems: inflate all four tyres to the correct pressure (check the door jamb sticker). Drive at above 25 km/h for several minutes. The light should go out automatically within one to two trips.
For indirect TPMS systems: inflate all four tyres to the correct pressure, then use the reset button (usually in the glovebox or under the dash, or via the dashboard menu) to reset the baseline. Consult your owner's manual.
If the light stays on after inflating and driving, a sensor fault or slow puncture is likely.
TPMS and Tyre Changes
When you rotate tyres or fit new tyres or sensors, a direct TPMS system must be reprogrammed to recognise the sensor IDs in their new positions. This is done with a TPMS tool — many NZ tyre shops include this service. Failing to reprogram means the system may show incorrect readings or remain in fault mode.
TPMS sensor battery life: Direct sensors use lithium batteries that are not field-replaceable. When the battery dies (after 5–10 years), the entire sensor must be replaced — typically at tyre change time.
WoF and TPMS
A TPMS warning light that is on at the time of inspection is generally assessed as a system fault. While NZTA's WoF rules focus on the physical tyre condition rather than the monitoring system, some inspectors will note a permanently illuminated TPMS light. More importantly, an illuminated light usually indicates a tyre pressure issue that will result in a WoF fail for the affected tyre.
How Much Does TPMS Service Cost in NZ?
| Service | Estimated NZD Cost |
|---|---|
| TPMS sensor replacement (per sensor) | $80–$160 (sensor + programming) |
| TPMS system reset/reprogram (after tyre change) | $30–$60 |
| Indirect TPMS reset | Often free at tyre shops |
When to Book a Mechanic or Tyre Shop
- Immediately if the TPMS light comes on — check tyre pressures before driving further. A significantly underinflated tyre can fail suddenly at motorway speeds
- Within a few days if pressures are correct but the light stays on — a sensor fault needs diagnosis
- At every tyre change — ask the shop to service and reprogram TPMS sensors