What you'll learn:
- A background on TPMS
- Different kinds of TPMS
- Current sensor technology
- Common TPMS tools
- What is ahead for the technology
One of man’s greatest ideas is the wheel, invented about 3,500 years ago. First used for wheelbarrows, chariots, and eventually carts and wagons, early examples were made of stone or wood and were improved upon by first adding leather, iron, and steel bands to wooden spoked wheels (Figure 1).
Solid rubber tires appeared in the mid-1800s (the first run-flat tires) and were excessively heavy and did not provide a smooth ride. Although not invented by him, John Dunlop is credited with creating air-filled (pneumatic) tires in 1888. In that same year, the first gasoline car (patented by Carl Benz in 1886) was fitted with metal tires covered with air-filled rubber. The tire tread was added in 1905 to protect the tire’s carcass from direct contact with the road and improve traction.
The air-filled tire was also the start of "flat tire anxiety" experienced by drivers worldwide, worrying about their tires losing air. The fear and inconvenience of tires going flat and having to mount a spare tire has led to tire pressure monitoring systems or TPMS.
TPMS history
It is estimated that around 25 percent of U.S. vehicles operate with underinflated tires, and fuel economy, tire longevity, handling, and safety all pay the price for low tire pressure. Auto manufacturers addressed this in 1986, when Porsche was the first car to feature a factory TPMS system and Renault was the first manufacturer to produce high-volume vehicles (2000 model year) that came standard with TPMS. The 1997 C5 Corvette was the first U.S. production vehicle to have TPMS as standard equipment, and because it lacked room for a spare tire, it was equipped with Goodyear run-flat tires.
In 2000, Firestone Tires and the Ford Motor Company recalled 14.4 million tires because of vehicle rollovers, caused by tire tread separation. These tire failures were linked to more than 250 deaths starting in the early 1990s and put pressure on the U.S. Congress to pass the Transportation Recall, Enhancement, Accountability, and Documentation (or TREAD)Act . The TREAD Act mandated TPMS technology for all light motor vehicles under 10,000 lbs. from September of 2007 on. The European Union adopted the same regulations in 2012.
TPMS alerts drivers when tire pressure falls below more than 25 percent of recommended inflation pressure. Early TPMS did not display actual tire pressure, and many drivers assumed that if the warning light was off, tire pressure must be good—this is not true. For example, if tire pressure in a passenger car is supposed to be 32 psi the TPMS light will not come on until pressure has dropped to 24 psi. If light truck tire pressure is recommended at 80 psi the driver will not be warned until the pressure drops to 60 psi. In either case, load capacity is significantly reduced before the driver is warned, and depending on driving conditions, it could cause severe tire damage or an accident (Figure 2).
Two flavors of TPMS
Direct TPMS (dTPMS) uses a sensor to measure tire pressure. Indirect (iTPMS) uses input from ABS wheel speed sensors to approximate low tire pressure. This works because when air pressure is low the tire's diameter is decreased, which affects wheel speed (Figure 3).
Early iTPMS was not reliable, because if overall tire pressures were low, the system would not set an alert; tire size and road conditions could mislead iTPMS, causing a false alert or no alert. Current and future iTPMS are and will be more reliable because of advanced data analysis (software). Some iTPMS requires tire size to be entered via a diagnostic tool to accurately calculate tire pressure. After adding air to a low tire, changing/servicing tires, or tire rotation, most iTPMS has a RESET button and driving procedure to recalibrate the system.
The vast majority of vehicles use dTPMS systems rather than iTPMS. In general, dTPMS is found on domestic, some Asian, and European vehicles; iTPMS is used on some Asian and European vehicles. Professional TPMS tools, like the Autel MaxiTPMS TS508 or Continental’s Autodiagnos TPMS SE, will have a database listing which vehicles use what type of TPMS.
Aftermarket sensors
Introduced in 2007, the number of TPMS-equipped vehicles in the U.S. is estimated at around 205 million in 2021. Early replacement tire pressure sensors were often only available at OEM dealers at a cost of around $100. In the past 14 years, the aftermarket has responded with universal, programmable sensors and pre-programmed sensors that can replace numerous OEM sensors with only a few part numbers and at about half the cost.
This sensor technology has reduced independent repair shops’ sensor inventory, making TPMS service more efficient. Sensors are available as “clamp-in” (retaining nut at the base of a metal valve stem) and "snap-in" (rubber) valve stems. On some applications, they can even be used as a replacement for older "band" style TPMS sensors.
One example of new sensor technology is the MX 1-Sensor by Autel. The company provides full-function TPMS diagnostic tools, sensors, and professional scan tools. The universal, programmable 1-Sensor combines both 315MHz and 433MHz frequencies into one TPMS sensor that provides coverage for 98% of vehicles. The patented PRESS release valve stem design allows rubber and metal valve stems to be interchanged using no tools (Figure 4).
The MX 1-Sensor can be programmed wirelessly, even when sensors have already been mounted to the wheel. Sensors are 100 percent cloneable with no relearn required when cloned with the original sensor ID and mounted in the same position on the vehicle. Using Autel’s latest TPMS tools, up to 16 sensors can be programmed at one time, and sensors can be updated for new vehicles applications via the tool.
The MX 1-Sensor is certified to meet SAE standards and is guaranteed for 24 months or 24,000 miles. For quality control tracking of a series, the number is imprinted on the sensor and can be read with Autel TPMS tools. A single sensor retails for around $43, and wholesale costs are $39.95 per sensor. In some markets, Autel has a promotion for 20 sensors and their TS508 TPMS tool for $895.
The Continental REDI-Sensor is another example of aftermarket TPMS sensors. The company offers both snap-in and clamp-on type sensors that are direct replacements for 280 OE sensors, covering over 138 million vehicles. They are preprogrammed for an entire range of vehicles and come ready to use out of the box. Labor time for installation is saved because no sensor programming is required (Figure 5).
REDI-Sensor works with all major TPMS scan tools, including ATEQ, Bartec, and Snap-on. REDI-Sensor is designed to follow existing OEM vehicle relearn procedures with no added steps. The REDI-Sensor pivoting metal clamp-in valve stem makes installation easier and accommodates a wide range of wheel rim profiles. REDI-Sensor replacement parts and service kits are available and include seals, washers, valve cores, hex nuts, and caps. Replacements are also available for the sensor’s metal valve stem.
Continental Commercial Vehicles & Aftermarket has a warranty registration website for REDI-Sensor Multi-Application TPMS Sensors. The website allows shops to register REDI-Sensors installed on customers’ vehicles. Technicians can use the information to alert customers of their warranty status and to file a warranty claim. The site stores customer names and addresses as well as their vehicle's year, make, model, date of sensor installation, serial number, and part number.
TPMS service
TPMS sensors don’t broadcast a continuous signal but only transmit when the vehicle is in motion, and even then, the signal is intermittent to conserve battery life. How long a vehicle is parked vs. how much it’s driven will affect battery life. Batteries inside TPMS sensors last anywhere from five to 10 years, with five to six years representing a more typical lifespan. Some scan tools can read battery data, but there is no industry standard regarding what battery information (if any) will be displayed (Figure 6).
Economically, it makes sense to replace sensors when new tires are installed. The dilemma is that after operating long enough for the tires to wear out, the batteries may not last through another set of tires. It’s a tough sell to customers: change the sensors with a new set of tires (adding $200 to the bill) or wait until the sensor batteries go dead, then have to pay for mounting/balancing, plus the new sensors. An effective approach to upselling customers TPMS sensors with a new set of tires is to stress safety. In addition to warning drivers of an underinflated tire, TPMS reduces risks of accidents due to tire failure and increases fuel economy and tire life. If a single sensor has reached the end of its lifespan, replacing all sensors at the same time is recommended—once one sensor’s battery dies, the rest are likely to be close behind.
One cause of TPMS sensor failure is galvanic corrosion. This affects the clamp-in type of sensor that uses a metal valve stem with a nut at its base to mount the sensor to the wheel. Exposure to road salt and moisture can weaken metal valve stems, which could lead to a sudden loss of tire pressure. TPMS sensor service kits for metal stems include hex nut, grommet/seal, valve core, and cap. Rubber stem valve kits include a new stem, valve core, and cap. These parts should be replaced when repairing a flat tire and mounting new tires. Do not replace a TPMS stainless steel valve stem core with one made of brass (Figure 7).
Always check the spare tire to determine if it’s TPMS-equipped and working properly.
If the spare tire sensor is not relearned or serviced, it typically results in a comeback. Replacement TPMS sensors must be relearned to the vehicle, plus a relearn may also be required after performing a tire rotation (Figure 8).
When a vehicle is in for service, check the TPMS alert light and document the presence of any illuminated or blinking light before performing any work. A steady light usually means that one or more of the tires has low air pressure and needs to be inflated. A warning light that flashes for 60 seconds (then stays on) can indicate a variety of issues including incorrect sensor installed, missing sensor, damaged sensor, or dead sensor battery.
TPMS tools
The Autel TS508 is a new generation TPMS diagnostic/service tool that will: activate TPMS sensors, read sensor status, check TPMS system health, program MX-sensors and conduct TPMS relearn. The TS508 is a minimum level, professional tool for individuals, or as a second TPMS tool for a busy shop. The tool costs $270 (wholesale). The TS508K kit ($329.95) comes with the tool and eight sensors and is a good starting point to experience Autel’s TPMS products (Figure 9).
The TS508 has two modes: TPMS Quick Mode: basic TPMS functions to check sensors and program MX-Sensors quickly and, TPMS Advanced Mode: TPMS sensor check, TPMS diagnostics, and sensor position relearn. Programming Autel MX 1-Sensors with the TS508 is easy and up to 16 sensors can be programmed at one time. Because the sensors are programmable any programing mistakes are easily fixed using the tool. TPMS relearn procedures are stored in the tool for U.S., Asian and European vehicles. The tool can be updated online at no cost after product registration.
Continental’s Autodiagnos TPMS SE tool is designed for shops with multiple bays and the need for more than one tool. It provides coverage for all passenger vehicle OE sensors and the most popular aftermarket sensors. TPMS and tire service functions can be accessed from the main screen without requiring vehicle-specific configurations where applicable. The tool can read and clear TPMS codes and has a VIN scanner for faster make/model/year lookups. The TPMS SE tool offers a graphical user interface that allows it to be used in a variety of lighting conditions including direct sunlight (opening image).
The SE professional-grade tool triggers and reads data from all OE vehicle sensors and has relearn-coverage for 99 percent of domestic, Asian, and European passenger vehicles. It provides direct (OBD, auto, manual) and indirect TPMS relearn procedures and performs OBD-II mode relearning via a cable connection. The SE tool displays data including sensor ID, tire pressure/temperature, and sensor battery status.
The future of TPMS
Between 2007 and 2021 more than 205 million vehicles were sold in the U.S. All of these cars and light trucks were required to have TPMS. Multiplying that number times four tires per vehicle results in 822 million TPMS sensors — that’s a lot of potential dollars for the automotive repair industry.
The future of TPMS technology is ever-changing as onboard systems become more dependent upon each other for efficiency and performance. Lindsay Smith, Continental REDI-Sensor product manager, recently said, “Several TPMS innovations will be introduced to mass vehicle production over the coming years, most notably Continental’s Electronic-Tire Information System (eTIS) that can be integrated into the inner liner of the tire allowing for installation on any tire regardless of type or rim size. This solution also has scalable features such as load and tread depth monitoring, possible integration with the chassis network processing.”
TPMS sensors are constantly draining their batteries, becoming damaged during tire repairs, replacements, rotations, and from corrosion. This represents a huge opportunity for repair dollars to flow into a repair shop—don't send your customers to the dealership for TPMS service. Invest in the tools, training, and parts inventory to service TPMS.
