The Tire Pressure Monitor System, known as TPMS, is the system of sensors built into automobiles since 2008 which tells you when you’re losing air from a tire.
TPMS systems are a result of fuel economy standards, as manufacturers are required to seek the highest possible fuel efficiency – also known as miles per gallon. Having properly inflated tires is a key component of fuel efficiency. Tires are inflated by psi, or pounds per square inch. For every one psi error, one-tenth percent of fuel efficiency (gas mileage) is lost.
Proper tire pressure is also crucial to your tire longevity. If one tire is low or too high, others will not turn evenly, resulting in uneven wear and premature need for replacement. Blowouts – sudden tire explosions while in motion – can also result from improperly inflated tires, resulting in loss of steering control and rollover accidents.
TPMS Monitor Lights
If your vehicle is equipped with a TPMS sensor system, lights on the dashboard should tell you when a tire issue is detected. Some vehicles show exactly which tire has an issue, while others are general, and you have to figure it out by yourself.
If you check all of your tires and they show proper inflation, the issue may be the TPMS sensors themselves.
Types of TPMS Systems
There are two types of tire pressure monitoring systems, direct and indirect. Both have batteries on the tire sensors that wirelessly send a signal to the car’s computer when a tire’s pressure is incorrect.
- Direct is the most common type of system, which uses sensors inside each tire, often part of the valve stem.
- Indirect has sensors in the anti-lock braking system that detect the speed of a tire’s rotation.
How to Check Tire Pounds Per Square Inch (PSI)
Inside the driver’s door of every vehicle is a sticker that shows important information about the vehicle, including the proper psi for all tires. Note that front and rear tires may have different psi levels. Using a handheld tire pressure gauge, check the pressure on each tire by pressing the gauge to the open valve stem (where air can be inserted).
If one or more tires does not have proper pressure, insert more air at the valve stem. If the gauge shows the tire has too much air pressure, you can release some by pressing on the center of the valve stem. Using the handheld gauge check the psi again after releasing air to ensure the proper pressure.
If tire psi continues to show errors after resetting them multiple times, it might be worthwhile to go to a mechanic for a quick check. Mechanics have OBD tools, which read sensor codes. Using this gadget the mechanic may be able to narrow the issue and even determine if the onboard computer has a problem rather than the tire sensors.
Calibrating TPMS
Check your owner’s manual for TPMS calibration instructions. Some vehicles allow drivers to reset the calibration from the driver’s seat, using buttons on the steering wheel. Others, like Toyotas, may have a button in the glovebox that has to be pressed while the ignition key is “on” but the engine is off. Once the indicator light goes off, the system is reset, but the process isn’t complete until the car has been driven at about 20 mph for an hour. If the indicator light turns on again after that period you can either repeat the tire pressure process and reset the system again or see a professional.
TPMS Sensor Issues
Like any vehicle systems, malfunction is possible, and TPMS is susceptible to:
- corrosion from exposure to salt on the road
- damage (hitting a curb, or pothole, etc.)
- malfunction if larger or smaller tires are installed
- extreme changes in weather (hot or cold).
Unfortunately it may take several rounds of resetting to get the system to work once the tire pressures are all corrected. If the system does not work after that, you may have to replace a sensor.
Replacing TPMS Sensors
Before undertaking the job of replacing sensors, either borrow or purchase an OBD tool to determine if the issue is with the individual tire or with the car’s onboard computer receiving information from the tires. These OBD tools must be plugged into the car’s computer system, and the codes deciphered. Sometimes a free diagnosis is available at an auto parts store.
Replacing an indirect sensor, which is attached to the antilock brake system, requires removing the tire. Experts say the battery in the indirect sensor can wear out after five years, requiring replacement. This extraction and replacement is most complex, as wiring is involved. Most experts suggest taking the vehicle to a qualified mechanic for replacement of this component.
Replacing a direct sensor requires first determining what kind of sensor was installed and where. Direct sensors can be inside tires or inside valve stems. Replacing sensors is an involved process that can require breaking the bead of a tire (taking it off the rim), a difficult task even with the right tools and knowledge.
Direct sensors can be mounted inside tires in several ways. Replacing one requires removing the tire and taking it off the rim to access the inside of the tire. The easiest replacement is the sensor that’s attached to the base of the valve stem. To replace this, simply unscrew the valve stem from the outside and replace the entire sensor and valve, then replace the tire on the rim.
Other direct sensors are mounted inside the tire on a cable. When replaced, ensure the cable is secured so it doesn’t come loose and become a new problem.
It’s crucial to replace a burned out sensor with exactly the same type of sensor so that it communicates correctly with the vehicle’s onboard computer.
After sensors are replaced, the system needs to be recalibrated using the buttons in the cabin. If a low tire pressure light persists, repeat the process or see a mechanic.
Getting a mechanic to identify and mitigate common car problems by replacing a sensor typically incurs a cost of around $200 for each tire, experts say. It’s good practice to have sensors replaced when getting new tires as the cost is smaller when it’s part of the overall job.
