Skip the auto shop - Our mechanics make house calls

How Does My Car Monitor Tire Pressure?

tire pressure monitor

You’re driving home from work and your steering wheel begins to pull. It gradually gets worse, then you hear a thump-thump-thump noise. You stop on the side of the highway to investigate, only to find you’ve got a flat tire. You realize you shouldn’t have ignored that tire pressure warning yesterday (and again this morning).

In the past two decades, tire pressure monitoring systems have transformed from being a fancy system on luxury cars to mandatory in all light vehicles in the United States. In 2007, legislation was passed requiring automakers to incorporate direct or indirect tire pressure monitoring systems in every one of their vehicles under 10,000 lbs in an effort to ensure safety and efficiency for motorists.

How Tire Pressure Monitor Systems Work

There are two styles of tire pressure monitors: direct and indirect.

Indirect Tire Pressure Monitoring

The most cost effective option for automakers to integrate into their vehicles is an indirect monitoring system. The system doesn’t actually check the tire pressures at all; it compares wheel revolutions on the four tires. An under-inflated tire rotates at a different rate than a properly inflated tire. The difference in rotational speeds is monitored by the anti-lock brake system (ABS) sensors and compared against each other. If one tire is reading differently, it triggers the tire pressure monitor’s warning light.

Direct Tire Pressure Monitoring

The direct monitoring systems are more user-friendly and accurate. In each tire’s air chamber, a sensor is mounted that reads the actual air pressure inside. Some sensors are mounted by a band around the circumference of the inside of the wheel, while most are integrated into the valve stem of each tire. Each sensor has an individual radio frequency identification code (RFID) that is transmitted to a receiver. The receiver doesn’t compare the tire pressures to each other; it compares the tire pressures to a threshold of allowable variance.

Which Tire Monitor System is Better?

The preferred system is the direct tire pressure monitor. This system analyzes the tire pressures individually and compares them with the threshold of the tire’s operating pressure. There is a downside to this system as well. Each sensor is equipped with a battery that can eventually die. Sensor replacement is often required as batteries aren’t always serviceable, and the cost of replacement can be a hundred dollars or more each.

The indirect tire pressure monitor is still a fairly effective system; however, it is more primitive and can be misleading. If two or more tire pressures drop evenly as is the case in fall and winter climates, the system doesn’t detect a difference in tire pressures and won’t trigger the warning light. As well, indirect systems don’t indicate which tire is low on pressure; it’s just a general system warning. This can lead to problems as the load capability on an insufficiently inflated tire is significantly lower than properly inflated tires.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

P0222 OBD-II Trouble Code: Throttle/Pedal Position Switch/Sensor B Circuit Low Input
P0222 code definition Throttle/Pedal Position Switch/Sensor B Circuit Low Input What the P0222 code means The manufacturer specifies a range of acceptable voltage to be produced from the throttle position...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Buy Fuel Treatments
Adding a fuel additive to your gas tank when you fill up is one way to clean vital engine parts of deposits, improve the performance of your engine,...


Related questions

Q: What Happens if I Overinflate My Tires?

Inflating tires to the correct pressure is one of the most important factors when inflating a tire. Both under and, over-inflating a tire can actually be detrimental to the performance of a vehicle and to the life of a tire....

Q: Question about damage to car

Hi. If your car has minimal or no body damage, a regular qualified mechanical technician can repair this situation. A body shop technician can also do this work, if they have mechanical technicians. Repair will probably involve damaged suspension, wheel...

Q: What is My TPMS Light For?

Many modern day vehicles, especially ones manufactured after 2007, are equipped with a TPMS or tire pressure monitoring system. You will see a TPM system in vehicles manufactured before 2007, but this is the year it became mandated for all...