How can you tell if a TPMS is defective?

A TPMS defect typically shows up as a stubborn warning light, readings that don’t line up with a manual tire check, or a fault indication in a diagnostic readout. If you notice these signs, the system could be malfunctioning and needs closer inspection.

TPMS, or Tire Pressure Monitoring System, is designed to alert drivers when a tire’s pressure is too low or when the system itself has a fault. There are two main types: direct TPMS, which uses pressure sensors mounted in each tire, and indirect TPMS, which uses ABS wheel-speed data to infer pressure changes. Defects can arise from weak or dead sensor batteries, damaged sensors or wiring, faulty receivers, or the need for a relearn after tire work. This article explains how to spot the signs, how to diagnose the issue, and what steps to take next.

What is a TPMS and how does it work?

Direct TPMS uses a battery-powered sensor in each tire to measure actual air pressure and transmit the data to the vehicle’s computer. Indirect TPMS relies on wheel-speed sensors and Vehicle Stability Control data to estimate pressure changes, without sensors in the tires themselves. Each type has its own potential failure modes, and understanding which type your vehicle uses helps in diagnosing problems.

Direct TPMS

In direct TPMS, a small sensor installed in the valve stem or Tire Pressure Sensor in the wheel reports pressure to the car’s system. The sensor battery typically lasts several years, and the sensor requires periodic maintenance if it leaks or becomes damaged. Replacing a failed sensor often involves programming or relearning to the vehicle.

Indirect TPMS

Indirect TPMS doesn’t measure pressure directly. It tracks differences in wheel speeds across tires to infer when one tire is underinflated. Because it relies on the ABS system, it can be fooled by tire size changes or abnormal wear and may require software updates or recalibration rather than sensor replacement.

Common signs of a defective TPMS

What drivers should watch for are the telltale indicators that something isn’t right with the system:

• The TPMS warning light stays on after you inflate all tires to the recommended pressures.


• The warning light flashes briefly, then stays solid, or returns soon after reset.


• TPMS readings shown on the dashboard don’t match the readings you get with a handheld tire gauge.


• One or more tires show a low-pressure warning even though a manual check confirms proper inflation.


• The system displays a fault or sensor readout (for example, “TPMS fault” or “Sensor fault”).


• A tire rotation or replacement requires a relearn, but the system won’t accept the new sensor IDs.


• Physical damage to valve stems or obvious sensor damage is observed during inspection.

If you notice any of these signs, you should proceed with a thorough check to determine whether the issue lies with the tire pressures, the sensors, or the system’s electronics. A faulty TPMS can compromise safety by giving false readings or failing to warn you of underinflation.

How to diagnose a TPMS

To systematically verify a TPMS, technicians follow a series of checks from manual pressure verification to sensor health and relearn procedures.

1. Check the actual tire pressures with a calibrated gauge on all four corners and compare them to the vehicle’s published specifications (usually found on the door jamb or owner’s manual).


2. Inflate each tire to the recommended pressure, then drive the car for a few miles to allow the system to recalibrate if it’s a direct TPMS or to recheck if it’s indirect.


3. Use a TPMS diagnostic tool or scan tool to retrieve fault codes, sensor IDs, and battery status for each tire sensor.


4. Inspect tires and wheel assemblies for leaks, damaged valve stems, or corroded sensor housings that could cause abnormal readings or communication faults.


5. For direct TPMS, test the sensors with a handheld tool to confirm they respond and report pressure correctly. If a sensor battery is dead or the sensor is damaged, replacement is typically required.


6. Perform a relearn or sensor programming procedure as required by your vehicle’s make and model after any sensor replacement or tire service.

Concluding note: If the readings align with the manual pressures but the warning persists, or diagnostic codes point to a specific sensor or module, the defect most likely lies with the TPMS hardware or software rather than the tires themselves.

What to do if a TPMS is defective

Once a TPMS defect is suspected, follow these practical steps to resolve the issue safely and efficiently:

• Have a qualified technician perform a diagnostic scan to retrieve TPMS fault codes and confirm sensor status.


• Replace defective components, such as damaged sensors or batteries, recognizing that many TPMS sensors have sealed batteries that are not easily replaceable in the field.


• Complete the required TPMS relearn procedure after sensor replacement or tire service so the system recognizes the new sensor IDs.


• Inspect tires for leaks, cracks, or damage and repair or replace as necessary to ensure accurate readings.


• Ask about the potential cost, warranty, and whether OEM or aftermarket sensors are recommended for your vehicle.

Final thought: Driving with a malfunctioning TPMS is riskier than dealing with the issue promptly. A correctly functioning TPMS helps you maintain proper tire pressures, improve safety, and optimize fuel efficiency.

Summary

TPMS defects manifest as persistent warning lights, mismatched readings, or fault messages. Understanding whether your vehicle uses direct or indirect TPMS helps tailor the diagnosis. Start with a manual pressure check, then use diagnostic tools to identify faulty sensors or modules, and perform the necessary relearn after any replacement. Regular maintenance and timely professional service are key to keeping the system reliable and your tires properly inflated.

How do I know if my pressure sensor is bad?

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Will unplugging the battery reset TPMS?

Disconnecting the car battery can temporarily reset the TPMS light by clearing its error memory, but it does not fully reset the system or its sensors, and the light may return after driving. For a proper reset, especially after adding air or replacing sensors, you need to follow the specific relearn procedure for your vehicle, which may involve driving or manually triggering the reset button after a full tire pressure adjustment. 
This video demonstrates how to disconnect the battery to reset the TPMS light: 59sSimple Mechanic AdviceYouTube · Oct 16, 2024
How to properly reset your TPMS

• Check and adjust tire pressure: Inflate all tires to the pressure recommended on your driver's side door jamb, or slightly higher, before any reset procedure. 
• Drive the vehicle: For many cars, driving at speeds over 50 mph50 mph50 mph for at least 10 minutes will trigger the system to re-read the pressure and turn off the light. 
• Use the TPMS reset button: Find the TPMS reset button, which is often located under the steering wheel. With the car in the "on" position (engine running or not, depending on the vehicle), press and hold the button until the light blinks three times. 
• Disconnect the battery (for a hard reset): If the other methods don't work, a temporary fix can be to disconnect the positive battery cable with the car off. Turn the ignition to "on" and honk the horn for a few seconds to drain any residual power. Reconnect the battery and start the car. 

Important considerations

• Temporary fix: Disconnecting the battery will only clear the light temporarily. The system will likely not have registered the correct tire pressures and the light will come back on. 
• Sensor issues: If the light comes back on after a proper reset, it could indicate a failing sensor battery or a faulty sensor. 
• Professional tools: For sensor registration after replacement, an OBD-II scanner is often required. 

What happens when a TPMS sensor goes bad?

When a TPMS sensor goes bad, the main consequence is inaccurate or no tire pressure information, which can lead to reduced fuel economy, premature tire wear, and compromised handling and safety. The most immediate sign is a flashing TPMS light on the dashboard, indicating a system malfunction rather than a specific tire needing air. 
Immediate effects

• TPMS warning light: The TPMS light on the dashboard will typically flash for 60-90 seconds when you start the car, then may turn solid. This indicates a malfunction in the system itself, not that a tire is low on air. 
• Inaccurate readings: The system will stop providing reliable data, so the tire pressure displayed on your dashboard will be incorrect or show no data at all for one or more tires. 

Safety and performance issues

• Reduced handling and braking: Improperly inflated tires, which a bad sensor won't warn you about, can negatively affect your vehicle's handling and braking efficiency, especially during emergency maneuvers.
• Increased accident risk: Ignoring the lack of proper tire pressure monitoring increases the risk of accidents, particularly blowouts, which can happen if a tire is severely under-inflated. 

Long-term costs

• Lower fuel efficiency: Under-inflated tires have higher rolling resistance, forcing the engine to work harder and use more fuel.
• Premature tire wear: Driving on under-inflated or over-inflated tires due to a bad sensor leads to uneven wear and reduces their lifespan, requiring more frequent replacement. 

What to do

1. Check tire pressure: Manually check the pressure in all tires with a reliable gauge and inflate them to the recommended level. 
2. Reset the TPMS: Inflating the tires correctly may resolve the issue in some cases. 
3. Visit a professional: If the warning light continues to flash, have a mechanic or tire shop inspect and replace the faulty sensor. It is often recommended to replace all sensors at the same time, as the batteries in the other sensors are likely to be nearing the end of their life as well. 

How do you diagnose a bad TPMS sensor?

Fill each tire until it reaches its recommended tire pressure. Then, gently release air from each tire and monitor the car display panel. If you release pressure from one tire and it doesn't trigger the system, it might mean that the sensor is defective.