What Does It Mean When It Says Service Tire Monitor System?

Damaso
| Last Updated: March 14, 2021

What the Tire Pressure Monitor System (TPMS) tries to tell you when lit is that at least one of the tires is underinflated/overinflated.

In that regard, you might be wondering what is the possible outcome of ignoring that warning, or if It is safe to deactivate the TPMS to save on repairs.

Those are just some of the questions we will answer throughout this article.

Photo credit: tirereview.com

How Does TPMS Work?

The principle of operation of the TPMS varies according to whether it is a Direct System or an Indirect System. We will briefly review each of them below.

Direct TPMS

The main feature that separates Direct TPMS from Indirect TPMS is that they use special sensors mounted on each wheel. Whether the vehicle is equipped with Banded, Clamp-in, or Snap-in sensors, they serve the same purpose of measuring the air pressure in each tire. Moreover, depending on the manufacturer, these sensors can also read the air temperature for an even more accurate value.

In vehicles equipped with Direct TPMS, the receiver is constantly collecting data from each sensor in time intervals that vary depending on the transmission mode the sensor is in (in most vehicles, every minute when in rolling mode or every 30 minutes or more in stationary/sleep mode).

Most Direct TPMS uses the difference in the strength of the RF signal received to determine each sensor’s location. Furthermore, the receiver is also pre-programmed with each sensor’s IDs to tell which one has low air pressure at any given time. In short, thanks to these sensors, the TPMS receiver can alert the driver when the pressure of any tire drops 20%-25% of its Cold Inflation Pressure.

Due to Direct Tire Pressure Monitoring Systems’ nature, every time the tires are rotated or serviced, the TPMS receiver must be resynchronized. This can be done thanks to TPMS Learn Mode, which is a procedure used both to relearn the position of each sensor and/or to add the ID of the new sensor to the system. Depending on the vehicle make, model, and year, the resynchronization can be automatic (automatic learning) or manual, which in some cases requires expensive scan tools.

All in all, Direct TPMS are very sophisticated, to the point that many can display individual tire pressure/temperature in the dashboard.

Indirect TPMS

As mentioned above, these systems do not have dedicated sensors on each tire to measure air pressure. Instead, Indirect TPMS uses the anti-lock brake system’s speed sensors to infer when a tire has low air pressure. Using the tire diameter and vehicle speed as a reference, the TPMS receiver calculates each wheel’s expected rotational speed. So, when the brakes are not applied, and one or more of the tires rotates at an abnormal speed, the receiver activates the instrument panel’s low tire pressure warning.

While these systems are not as accurate as Direct TPMS, they serve the same function of alerting the driver of a possible safety risk due to a flat tire. Furthermore, since Indirect TPMS do not have air pressure sensors, they are cheaper to manufacture than Direct TPMS and require less maintenance. However, they must be reset after inflating tires or performing routine tire rotation.

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Pros of TPMS on Vehicles

Regardless of the type of TPMS, be it Direct or Indirect, both offer significant benefits, which we will discuss in detail in this section.

Improves Your Safety

While TPMS is not a substitute for a periodic tire inspection, they certainly provide you with a noticeable improvement in safety by warning you when a tire has low air pressure. In fact, the NHTSA estimates that TPMS reduces the chance of driving with an underinflated tire by 56%.

Increases Fuel Economy

It's no secret that the air pressure in the tires has a huge effect on fuel consumption. This has a lot to do with the area of contact of the tread with the pavement and the effective diameter of the tire. An underinflated tire has a smaller diameter so it rotates a greater number of times per minute which impairs fuel consumption. On the other hand, the tread of an overinflated tire has a smaller contact area with the pavement, increasing fuel consumption.

Extends Tire Life

Maintaining the proper air pressure in the tires helps to extend their life significantly. The sidewalls of tires are especially prone to premature damage when pressure is low. This is due to the weight of the vehicle exerting an excessive force on them. The tread is also sensitive to air pressure values below what is stipulated by the manufacturer. Among many causes, this is motivated by the difference in the tire’s internal temperature and the area of contact with the pavement.

Cons of TPMS on Vehicles

Despite offering safety and fuel economy advantages, TPMS also has some disadvantages. In this section, we will review the most important of them.

Prone to Damage

While technically speaking, both the sensors and the receiver of the TPMS are designed to last many years, in practice, their longevity can be affected by their vulnerability when handled by inexperienced hands. Since the TPMS sensors are attached to the tire valve in most cases, they are prone to break when servicing the tire. Moreover, in some cases, just by damaging the valve stem, the sensor will have to be replaced. On top of all that, some TPMS sensors can be affected by tire sealants like Fix-A-Flat.

Require Resynchronization

One of the most annoying aspects of TPMS is its need to resynchronize or reset the system each time the tires are rotated. While it is true that the latest generation TPMS can be reset easily, it is also true that many vehicles require expensive diagnostic tools to carry out this process.

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Can You Deactivate Tire Pressure Monitoring Systems?

For better or for worse, it is possible to disable the Tire Pressure Monitoring System in some vehicles.

This is done either by disabling the low tire pressure warning light on the dashboard or by using special devices that 'emulate' the RF signal coming from the TPMS sensors and thus mislead the receiver. That said, it's worth looking at all the pros and cons of taking such action.

Let's start with the benefits of bypassing the TPMS.

  • It saves you from the cost of replacing one or more sensors when they become damaged.
  • Some of these systems are wireless and do not require modifications or reprogramming.
  • Allows you to change tires without the need to synchronize the system.

Saving money is always tempting. However, in our opinion, the risks associated with removing TPMS are high.

  • When you disable the TPMS you spend more money on fuel, tires, and brakes. 
  • Disabling the TPMS could have legal consequences. It should not be ruled out that fees might be applied to the owners of vehicles with the TPMS inoperative in the not too distant future. This without mentioning the economic and legal consequences in the event of a traffic accident where it is shown that the system was disabled.
  • When you bypass the TPMS, you put your safety at risk since you will drive the vehicle without knowing for sure if your tires are underinflated.

Tire Monitoring System Terminology and Common Concepts

It is essential to understand the terminology and basic concepts of TPMS:

  • Advanced TPMS System: cutting-edge TPMS systems that include a dashboard display that shows individual tire’s pressure/air temperature. 
  • Aspect Ratio (Tire): refers to the ratio between tire section height and tire section width. This ratio is important since it is directly associated with the recommended tire inflation pressure.
  • Automatic Learning: a feature included in the most recent TPMS which enables the system to automatically learn/relearn the sensor IDs while the vehicle is being driven.
  • Banded TPMS Sensor: a type of TPMS sensor that is mounted in the wheel's inner surface at 180 degrees from the valve stem.
  • Basic TPMS System: most common TPMS systems, using a yellow dashboard telltale to inform the driver about low tire pressure and/or system malfunctions.
  • Clamp-in TPMS: a type of TPMS sensor that is attached directly to the Schrader valve. In some cases, the sensor and valve are one piece, so if the valve stem is damaged, the entire assembly would have to be replaced.
  • Cloning: is the procedure used to copy an existing sensor ID number to a programmable TPMS sensor (which is usually generic) with the help of a cloning tool. In the eyes of the receiver, the sensor remains the same since it has the same ID.
  • Cold Inflation Pressure (placard pressure): is the vehicle manufacturer’s recommended tire inflation pressure when the tire is "cold.” The tire is assumed to be "cold" when it has not been in motion for at least 3 hours. This value is also known as "placard pressure" since in late-model vehicles it is mandatory to indicate this value in a plate or decal on the driver side door jamb.
  • Configurable TPMS: most aftermarket TPMS sensors can be programmed (configured) to be used in a particular vehicle with the help of a scan tool.
  • Delta Pressure: some systems require a quick air pressure change (usually +/- 2 PSI) to trigger the TPMS sensors during the learn/relearn process; this is known as the “delta pressure”.
  • Direct [TPMS] System: these systems measure the air pressure/temperature within each tire using independent sensors designed for this purpose.
  • ID Number: is an identification number unique to each sensor. 
  • Indirect [TPMS] System: unlike Direct TPMS, these systems do not have air pressure/temperature sensors but instead use the sensors of the anti-lock braking system to determine the rotation speed of each wheel and thus determine which tires ‘could’ have lower pressure than the rest.
  • Learn Mode: it’s a special mode in which the TPMS receiver learns/relearns both the ID and each of the tire sensors’ positions. Its activation may require either a manual procedure or a scan tool, depending on the vehicle.
  • Low-Pressure Warning Telltale: this is the TPMS warning light that usually lights when the air pressure on any tire is below 25% of the pre-programmed placard pressure.
  • Magnet Trigger: a magnet used on some vehicles to trigger a specific TPMS sensor once placed around the valve stem.
  • OE Sensor: a genuine TPMS sensor designed and fabricated according to the Original Equipment Manufacturer (OEM) specifications. Usually, these sensors are pre-programmed for a specific vehicle.
  • [TPMS] Protocol: the software layer used to establish communication between TPMS sensors and the receiver. Most vehicle manufacturers use their own proprietary TPMS protocol.
  • Radio Frequency (RF): the wireless communication technology used by most TPMS sensors.
  • Receiver (onboard computer): the central module in charge of processing and interpreting the information coming from TPMS sensors. This is the same onboard computer that alerts the driver about a malfunction or low tire pressure situation via the dashboard.
  • Rolling Mode: as its name suggests, this is the mode used when the vehicle is in motion. While in this mode, the TPMS sensors generally send the air pressure/temperature information to the receiver once per minute.
  • Service Kit: a special kit including valve cores, valve caps, grommets, seals, washers, and more, depending on the TPMS sensor type. Although service kits are supposed to be used during each tire service, not all TPMS use them.
  • Sleep Mode: a special mode used by TPMS sensors to save battery. Generally, this mode is automatically enabled after several minutes without detecting motion.
  • Snap-in TPMS: a type of TPMS sensor that is attached to the wheel by a rubber-coated metal valve stem. Unlike clamp-in sensors, most snap-in TPMS sensors are serviceable.
  • TPMS: acronym for Tire Pressure Monitoring System
  • Wheel Well Trigger: a hardwired wheel well trigger used during learning mode by some newer vehicles with automatic sensor localization.

Conclusion 

Tire Pressure Monitoring Systems have an important mission, preventing car accidents by warning drivers when any of the tires have inadequate air pressure. Considering the risks associated with driving on underinflated or overinflated tires, should you ignore this warning? Definitely not. For this same reason, we do not advise deactivating the TPMS, even if this implies an additional cost when buying new tires.

People Also Ask

Do you still have doubts about TPMS? In this section, we will answer the most frequently asked questions.

How Much Does It Cost To Replace A Tire Pressure Sensor?

The average cost to replace TPMS sensors ranges from $100 to $300. Of that amount, only between $50 and $70 are labor, and the rest corresponds to the sensor’s cost. Given the high cost of TPMS sensors, many people opt for 'aftermarket' sensors, which have a significantly lower price. Our recommendation with aftermarket sensors is to make sure they meet OEM specifications.

How To Tell Which TPMS Sensor Is Bad?

Since each car manufacturer uses its own communications protocol, one of the easiest solutions to determine which TPMS sensor is bad is to take your car to the nearest tire shop so they can perform a complete check for you.

That said, depending on the make, year, and model of your car, you can get a TPMS Relearn/Reset Tools for as little as $13. These little devices allow you to trigger TPMS 'Learn Mode' and verify which of the sensors is transmitting and which is not. Alternatively, some diagnostic scanners may also access the TPMS module for testing.

Damaso

Damaso has been in the automotive world since he was 14 years old and his father decided to bought an auto repair shop. Years later, his passion for electronics, computers, and automotive mechanics motivated him to graduate in Mechanical Engineering and venture into the sales of automotive equipment. For years Damaso worked as a technical advisor assisting car dealerships, tire shops, and even the plants of Toyota and Mitsubishi that operate in his country. He has over 25 years of experience reporting on topics ranging from DIY jobs, technological analysis, automotive news, and more. He is a wealth of information and a valued member of our team.