How To Tell Which Tire Sensor Is Bad

Having a tire pressure monitoring system (TPMS) warning light illuminate on your dashboard can be frustrating. It signals a problem with one or more of your tire pressure sensors, but determining which sensor is faulty can seem like a daunting task. Accurately identifying the bad sensor is crucial to avoid unnecessary repairs and ensure your TPMS functions correctly, maintaining optimal tire pressure and driving safety. This article will walk you through the symptoms, root causes, and troubleshooting steps to pinpoint the problematic sensor.

Symptoms of a Failing Tire Pressure Sensor

The most obvious sign of a failing TPMS sensor is the TPMS warning light itself. However, understanding the specific behavior of the light and other accompanying symptoms can greatly assist in diagnosing the culprit. Here’s a breakdown of potential indicators:

Constant TPMS Light: A consistently illuminated TPMS light usually indicates that one or more of your tires are significantly underinflated, or that one of your sensors has failed to transmit data.
Flashing TPMS Light: A flashing TPMS light is often a sign of a system malfunction, not necessarily low tire pressure. This often indicates a problem with one or more sensors, the TPMS module, or a communication issue within the system. This is a more serious issue than a constant light.
Inaccurate Tire Pressure Readings: If your vehicle displays individual tire pressures, pay close attention. A sensor reporting an unusually high or low pressure compared to the other tires, especially when you know the tire is properly inflated (checked manually with a reliable gauge), suggests a potential sensor issue. Look for readings that are wildly inaccurate – a tire reading 0 PSI or 70 PSI when other tires are in the 30-35 PSI range is a clear red flag.
Intermittent TPMS Light: The light turns on and off seemingly at random. This is often indicative of a sensor with a weak battery or an intermittent connection problem. Temperature changes can often trigger this behavior as well.
TPMS Light On Only During Certain Conditions: Does the light only come on after driving for a certain amount of time? Or only when the weather is cold? This could point to a sensor whose battery is struggling to maintain a signal under specific conditions.
No Tire Pressure Readings Displayed: On vehicles that show individual tire pressures, you might see dashes (---) instead of actual pressure values for one or more tires. This almost certainly indicates a sensor that isn't communicating with the TPMS module.

Understanding the Root Cause: Why Sensors Fail

TPMS sensors are small, battery-powered devices located inside your tires. They continuously monitor tire pressure and transmit this data wirelessly to your vehicle's TPMS module. Several factors can contribute to their failure:

Battery Life: The most common cause of TPMS sensor failure is simply battery depletion. TPMS sensor batteries typically last for 5-10 years, depending on usage and environmental conditions. Once the battery dies, the sensor stops transmitting data.
Physical Damage: Tire changes, road debris, and even impacts from potholes can damage the sensor. The sensor can be internally damaged, or the valve stem can be bent or broken.
Corrosion: Exposure to moisture, road salt, and other corrosive elements can damage the sensor's internal components or corrode the valve stem.
Valve Stem Issues: The valve stem itself can leak, become clogged, or break. This can lead to inaccurate pressure readings or complete sensor failure. Aluminum valve stems are particularly prone to corrosion.
Installation Errors: Improper installation during a tire change can damage the sensor. Overtightening the valve stem nut or failing to use the correct tools can compromise the sensor's integrity.
Software Glitches: While less common, software glitches in the TPMS module itself can occasionally cause false readings or sensor communication issues.

What Happens If You Ignore a Faulty TPMS Sensor?

While driving with a TPMS light illuminated isn't immediately dangerous, ignoring it can have several negative consequences:

Reduced Fuel Efficiency: Underinflated tires increase rolling resistance, leading to lower gas mileage. Maintaining proper tire pressure, as monitored by the TPMS, optimizes fuel economy.
Uneven Tire Wear: Improper tire pressure causes uneven wear patterns, shortening the lifespan of your tires. This can lead to premature tire replacement.
Compromised Handling and Braking: Underinflated tires negatively affect your vehicle's handling and braking performance, especially in emergency situations. This increases the risk of accidents.
Delayed Detection of Leaks: A properly functioning TPMS alerts you to slow leaks that you might not otherwise notice. Ignoring the system means you could be driving on a slowly deflating tire, increasing the risk of a blowout.
Potential Safety Issues: In extreme cases, driving on severely underinflated tires can lead to tire failure, especially at high speeds.

Recommended Fixes: Pinpointing and Replacing the Bad Sensor

Here’s a breakdown of how to identify and address a faulty TPMS sensor:

Visual Inspection: Start with a visual inspection of all four tires and valve stems. Look for any signs of damage, such as cracks, leaks, or corrosion. Pay close attention to the valve stem on the wheel where you suspect the sensor might be failing.
Manual Tire Pressure Check: Use a reliable tire pressure gauge to manually check the pressure of all four tires. Compare these readings to the values displayed on your vehicle's TPMS (if available). If one tire consistently reads significantly lower than the others, even after inflation, the corresponding sensor is a prime suspect.
TPMS Reset/Relearn Procedure: Consult your vehicle's owner's manual for the TPMS reset or relearn procedure. Sometimes, a simple reset can resolve minor communication glitches. Follow the instructions carefully, as the procedure varies depending on the vehicle make and model.
Professional TPMS Scan Tool: The most accurate way to identify a faulty sensor is to use a professional TPMS scan tool. These tools can communicate directly with each sensor, read its data (including battery life), and identify any error codes. Most tire shops and repair shops have these tools. This tool will display specific sensor data, often including a "battery life" percentage or status.
Sensor Swapping (Advanced): If you suspect a particular sensor is faulty, you can try swapping it with a known good sensor from another tire (if you have a spare set or are comfortable dismounting and remounting tires). If the problem moves to the new location, you've confirmed that the original sensor is the culprit. Note: This is a more involved process and should only be attempted by experienced individuals.
Replacement: Once you've identified the faulty sensor, the best solution is to replace it with a new one. Ensure you purchase a compatible sensor for your vehicle make, model, and year. Most tire shops can handle the replacement process, including programming the new sensor to communicate with your vehicle's TPMS module.

Cost Estimates and Shop Advice

The cost of replacing a TPMS sensor can vary depending on several factors, including:

Sensor Type: Aftermarket sensors are typically less expensive than OEM (Original Equipment Manufacturer) sensors.
Vehicle Make and Model: Some vehicles require more specialized sensors, which can increase the cost.
Shop Labor Rates: Labor costs vary depending on the location and the shop's hourly rate.

Generally, you can expect to pay between $50 and $200 per sensor, including parts and labor. It's always a good idea to get quotes from multiple shops before proceeding with the repair.

When choosing a shop, look for one with experienced technicians and a good reputation. Ask if they have experience working with TPMS systems and if they use quality replacement sensors. A reputable shop will also be able to properly program the new sensor to your vehicle's TPMS module.

Consider replacing all sensors at once: If your vehicle is over 5 years old and you're replacing one sensor due to battery failure, it's often wise to replace all four sensors at the same time. This can save you time and money in the long run, as the other sensors are likely nearing the end of their battery life as well.

Credibility and Common Failure Points

While specific data on TPMS sensor failure rates is often proprietary, there's a good amount of collective knowledge and some manufacturer information available.

Common Mileage for Failure: TPMS sensors tend to start failing around 75,000 to 100,000 miles, or after 5-7 years of service. This aligns with the typical lifespan of the sensor batteries.

For example, older GM vehicles are notorious for corrosion of the valve stems leading to leaks and sensor failure. Specific years of Hondas (around 2008-2012) had issues with the TPMS control unit itself needing replacement due to communication errors even with good sensors. Searching online forums dedicated to your make/model vehicle may yield specific failure patterns in your vehicle.

Keep in mind that every vehicle is different, but understanding these common issues can help you in diagnosing your TPMS issues and finding a solution.