How To Know Which Tire Pressure Sensor Is Bad

Dealing with a faulty Tire Pressure Monitoring System (TPMS) can be frustrating. That little warning light on your dashboard can mean anything from a simple pressure adjustment to a completely failed sensor. Knowing which sensor is the culprit saves you time, money, and the aggravation of replacing perfectly good parts. In this article, we'll walk you through the telltale signs of a bad TPMS sensor and how to pinpoint the problem, ensuring you get back on the road safely and efficiently.

Symptoms of a Bad TPMS Sensor

A malfunctioning TPMS sensor can manifest in several ways. Recognizing these symptoms is the first step in diagnosing the issue:

TPMS Warning Light On: This is the most obvious sign. The light may be constantly illuminated, or it may flash for a minute or two upon starting the vehicle before staying on. A flashing light often indicates a system malfunction, which could be a bad sensor, while a solid light usually signifies low tire pressure.
Inaccurate Tire Pressure Readings: If you have a display showing individual tire pressures, compare these readings to the actual pressures using a reliable tire pressure gauge. A significant discrepancy (more than a few PSI) suggests a problem with that sensor.
Failure to Read Tire Pressure: The system might show a "--" or "0" reading for a particular tire, indicating the sensor isn't transmitting data.
Intermittent Warnings: The warning light might come on and off seemingly randomly, especially during temperature changes. This can be due to a weakening sensor battery or a loose connection.
TPMS Light After Tire Rotation: If the light illuminates after a tire rotation, the system may need to be reset or relearned to recognize the new sensor positions. However, if the light persists after relearning, it could indicate a sensor problem.
Sensor is physically damaged: Obvious signs of physical damage or corrosion of the sensor visible from the outside of the tire.

Root Cause: Understanding TPMS Sensor Failures

TPMS sensors are small, battery-powered devices mounted inside your tires, typically attached to the valve stem. They constantly monitor tire pressure and transmit this data wirelessly to your vehicle's computer. Several factors can contribute to sensor failure:

Battery Failure: TPMS sensors are battery-operated, and like all batteries, they have a limited lifespan, typically 5-10 years. Once the battery dies, the sensor stops transmitting data. This is the most common reason for sensor failure.
Corrosion: Moisture and road salt can corrode the sensor's internal components or the valve stem, leading to malfunction.
Physical Damage: Impacts from potholes, curbs, or debris can damage the sensor. Incorrect tire installation or removal can also damage the sensor or valve stem.
Valve Stem Issues: The valve stem itself can corrode or become damaged, leading to leaks and inaccurate readings. In some cases, the valve stem and sensor are integrated, requiring replacement of the entire unit.
Sensor Malfunction: Internal electronic components within the sensor can fail due to age, manufacturing defects, or environmental factors.
Communication Issues: Interference from other electronic devices or damage to the TPMS receiver in the vehicle can prevent the system from receiving signals from the sensors. While less common, this can mimic a sensor failure.

Ignoring a Faulty TPMS: The Consequences

While a TPMS warning light might seem like a minor annoyance, ignoring it can have significant consequences:

Compromised Safety: Underinflated tires can lead to reduced braking performance, decreased handling, and increased risk of tire blowouts, especially at high speeds.
Reduced Fuel Efficiency: Underinflated tires increase rolling resistance, forcing your engine to work harder and reducing fuel economy.
Uneven Tire Wear: Incorrect tire pressure can cause uneven wear patterns, shortening the lifespan of your tires and requiring premature replacement.
Potential for More Expensive Repairs: Continuing to drive with an underinflated tire can damage the tire's sidewall, making it unrepairable and requiring a new tire.
Failing Inspection: Many states include TPMS functionality as part of their vehicle safety inspections. A malfunctioning TPMS can result in a failed inspection.

Recommended Fixes: Pinpointing the Bad Sensor

Once you've identified the symptoms, the next step is to determine which sensor is failing. Here's a breakdown of the recommended steps:

Visual Inspection: Start by visually inspecting all four tires and valve stems for any signs of damage or corrosion. Look for cracks, bulges, or leaks.
Manual Pressure Check: Use a reliable tire pressure gauge to check the pressure in all four tires. Compare these readings to the values displayed by your TPMS (if available). Note any significant discrepancies. Inflate any tires that are below the recommended pressure (usually found on a sticker on the driver's side doorjamb).
TPMS Relearn Procedure: After adjusting the tire pressures, attempt to reset or relearn the TPMS system. The procedure varies depending on the vehicle make and model. Consult your owner's manual or search online for specific instructions. Sometimes, this simple step can resolve the issue, especially if the tires have been recently rotated or replaced.
Using a TPMS Scan Tool: A TPMS scan tool is the most effective way to diagnose a faulty sensor. These tools can read the sensor's ID, pressure, temperature, and battery status. The tool will display the sensor's data, allowing you to identify any sensors that are not transmitting or are reporting inaccurate information. Many auto parts stores offer free TPMS scans.
Professional Diagnosis: If you're unable to pinpoint the bad sensor using the above methods, it's best to consult a qualified mechanic. They have specialized equipment and expertise to diagnose complex TPMS issues.
Swap Test (Advanced): If you suspect a specific sensor but aren't 100% sure, and you're comfortable with some DIY, you *could* carefully swap the suspected bad sensor with one from a tire you know is working correctly (e.g., front to back on the same side). This requires breaking the bead of the tire and should only be attempted by experienced individuals. After the swap, relearn the TPMS. If the problem moves to the tire where you installed the suspect sensor, you've confirmed it's the culprit. Warning: This is not recommended for the average DIYer as improper tire handling can be dangerous.

Cost Estimates and Shop Advice

The cost of replacing a TPMS sensor can vary depending on several factors, including the vehicle make and model, the type of sensor (OEM or aftermarket), and the labor rate of the repair shop.

Sensor Cost: Aftermarket TPMS sensors typically range from $30 to $100 per sensor. OEM (Original Equipment Manufacturer) sensors can be more expensive, often exceeding $100 each.
Labor Cost: Labor costs can vary from $50 to $150 per tire, depending on the shop and the complexity of the job. This includes the cost of removing the tire, replacing the sensor, balancing the tire, and relearning the TPMS system.
Total Cost: The total cost to replace a single TPMS sensor can range from $80 to $250 or more.

Shop Advice:

Get Multiple Quotes: Before committing to a repair, get quotes from several different shops to compare prices.
Ask About Warranty: Inquire about the warranty on the sensor and the labor. A reputable shop will offer a warranty on their work.
Consider Aftermarket Options: Aftermarket TPMS sensors can be a cost-effective alternative to OEM sensors. Ensure the aftermarket sensor is compatible with your vehicle.
Check for TPMS Service Kits: Consider purchasing a TPMS service kit, which includes the valve stem, core, cap, and other necessary hardware. This can help prevent future leaks and corrosion.
Replace in Pairs or All Four: If one sensor is failing due to battery age, it's likely that the other sensors are nearing the end of their lifespan as well. Consider replacing all four sensors at the same time to avoid future problems and save on labor costs.

Credibility: TSBs and Common Failures

Vehicle manufacturers often issue Technical Service Bulletins (TSBs) to address common problems with their vehicles, including TPMS issues. Check online databases or consult a mechanic to see if any TSBs apply to your vehicle's TPMS system. Searching online forums dedicated to your specific make and model can also reveal common TPMS failure patterns reported by other owners.

For example, many vehicles experience TPMS sensor failures around the 5-7 year mark, coinciding with the typical lifespan of the sensor battery. Specific makes and models may have known issues with particular brands of sensors or valve stem corrosion. Consulting these resources can provide valuable insights and help you make informed decisions about your TPMS repair.