What Is Tyre Pressure Monitoring System (TPMS) & How Does It Work?

Tyre Pressure Monitoring System (TPMS)

The Tyre Pressure Monitoring System (TPMS) in your vehicle alerts you when one or more tyres are significantly under-inflated, potentially creating unsafe driving conditions. The low tyre pressure indicator appears as a yellow symbol on the dashboard, resembling a tyre cross-section (similar to a horseshoe) with an exclamation point.

This indicator light has a significant history, stemming from years of uncertainty about proper tyre pressure and numerous serious accidents that could have been prevented if drivers had been aware of low air pressure. Today, many vehicles still operate with under-inflated tyres, but proper tyre maintenance supported by a TPMS can help avert serious accidents.

Before the introduction of this indicator light, drivers had to physically check their tyre pressure by crouching down and using a tyre gauge, which was the primary tool available to most consumers.

Not all TPMS systems operate in the same manner. The illumination of the low tyre pressure indicator marks the final step in either an indirect or direct TPMS process.

Indirect TPMS: What Is It and How Does It Work?

An indirect TPMS utilizes wheel speed sensors from the anti-lock brake system to monitor the rate of revolution of each wheel. These sensors allow the on-board computer to compare wheel speeds with each other and other vehicle data, such as overall speed.

By analyzing the rotation rates, the computer can determine the relative size of the tyres. If a wheel spins faster than expected, the system infers that the tyre is under-inflated and alerts the driver.

Unlike direct TPMS, an indirect tyre pressure monitoring system does not actually measure tyre pressure electronically, as you would with a tyre gauge. Instead, it tracks the rotational speed of the tyres and triggers the indicator light if there are any discrepancies in the rotation.

Advantages of Indirect TPMS

- Cost-Effective: Generally less expensive than a direct TPMS.

- Lower Maintenance Needs: Requires less programming and maintenance over time compared to direct TPMS.

- Simpler Installation: Involves less overall installation maintenance than direct systems.

Disadvantages of Indirect TPMS

- Accuracy Issues: May become inaccurate if you switch to larger or smaller tyres.

- Reliability Concerns: Can be unreliable if tyres are unevenly worn.

- Reset Requirement: Must be reset after properly inflating each tyre.

- Post-Rotation Reset: Requires resetting after routine tyre rotations.

Direct TPMS: What Is It and How Does It Work?

Direct TPMS employs pressure monitoring sensors located within each tyre, measuring specific pressure levels rather than relying on wheel revolution data from the anti-lock brake system.

These sensors can also provide tyre temperature readings. The system sends this data to a centralized control module for analysis. If tyre pressure falls below the desired level, the information is transmitted wirelessly to your dashboard, illuminating the indicator light. Each sensor has a unique serial number, allowing the system to differentiate between its own readings and those from other vehicles, as well as among individual tyres.

Many manufacturers utilize proprietary technology for these specialized systems, so replacing a TPMS in a consistent and compatible manner requires the expertise of a knowledgeable technician.

Advantages of Direct TPMS

- Accurate Readings: Provides actual tyre pressure readings from inside the tyre.

- Consistent Accuracy: Not affected by tyre rotations or replacements.

- Easy Resynchronization: Simple process after tyre rotations or replacements.

- Long Battery Life: Sensors typically last about a decade.

- Spare Tyre Inclusion: May include sensors in the vehicle’s spare tyre.

Disadvantages of Direct TPMS

- Higher Cost: Generally more expensive than indirect TPMS.

- Tool Requirements: Resynchronization, while simple, may require costly tools.

- Non-Serviceable Batteries: If the battery is drained, the entire sensor must be replaced.

- Confusion Over Proprietary Systems: Installation, servicing, and replacement can be complicated for consumers and auto shops.

- Susceptibility to Damage: Sensors may be damaged during mounting or demounting.

Tyre Pressure and Safety

Although the methods may be different, both systems serve the same purpose and activate the same indicator light. Even though a TPMS can deliver accurate alerts when properly maintained, it’s not a replacement for manual air pressure checks, consider it just another item in your car maintenance toolbox.