Service Advisor: Airing Out TPMS Concerns: Q & A Forum -

Service Advisor: Airing Out TPMS Concerns: Q & A Forum

The following are some questions and answers that address today’s Tire Pressure Monitoring Systems (TPMS).

There are many factors that affect tire pressure, including ambient temperature changes and tire damage, such as punctures. In fact, tire pressure drops about 1 psi for every 10 degrees F drop in ambient temperature. Additionally, tires lose as much as 1.5 psi per month as air escapes the tire and rim naturally. The following are some questions and answers that address today’s Tire Pressure Monitoring Systems (TPMS).

What is one of the leading causes of sensor failure?
Corrosion: Sensors or sensor stems can be damaged by corrosion from road salts, moisture, missing valve caps or galvanic corrosion. The use of dissimilar metals or use of non-TPMS components can result in galvanic corrosion, which may affect the sensor’s ability to read or transmit data.

How many TPMS Sensors are on the road?

There are more than 220 million TPMS sensors now on the road. About 45% of the sensors are now at least five years old. It has been estimated that more than 10 million sensors will need to be replaced in the next two years.

What percentage of the sensors and systems can relearn on their own?

Less than 40% of the vehicles can re-set themselves. Many “Auto Learns” can only do one new TPMS Sensor. For the other 60 percent, these vehicles require an activation or activation/scan combination tool.

What are the common standards for TPMS systems?
There is no common standard for the TPMS sensors with variations including frequencies, modulations, data structure, communications protocols, mechanical fitment and many other factors. While U.S. law mandates that the TPMS must warn the driver when a tire is under-inflated by 25%, it did not specify any standards for the equipment.

What information is transmitted by the sensors?
The sensors transmit data such as their unique sensor ID, temperature and pressure, battery life and other diagnostic information.

How long do the batteries in the sensors last?

It depends on a variety of factors including the sample rate, drive cycle of the customer and even the environment. If a sensor transmits the pressure every 10 seconds,  it will not last as long as a sensor that transmits the pressure every 15 seconds. Some sensors may last as long as 10 years while some may last only three to five years.

How do I know if a vehicle is equipped with direct TPMS?

All vehicles manufactured after 2007 will have TPMS. If a Vehicle is equipped with TPMS, a lighted universal symbol on the dash will be illuminated when the ignition is turned to the “On” position. If this does not work, try using the learn and test procedure with a TPMS tool.

Remember, visually, a snap-in TPMS sensor looks very similar to a standard tubeless tire valve (TTV). Always check the owner’s manual or turn the ignition on and look for the universal TPMS symbol to determine if the vehicle has TPMS.

What does it mean if the TPMS warning lamp illuminates?
When the TPMS warning lamp on the instrument panel illuminates while driving, it means that the system has detected at least one tire with a pressure below the accepted minimum psi for the vehicle.
The tires should be inspected and the tire pressure checked as soon as possible. The lamp will extinguish after the tires are properly inflated.

What does it mean if the warning lamp goes on and off?
On cold mornings, the warning lamp may illuminate for a short period of time and then extinguish. This type of warning lamp response is likely caused by marginally low tire pressure that dips below the warning threshold over night, but rises to an acceptable level as the tires heat up through vehicle operation or an increase in ambient temperature. The tires should be inspected and the tire pressure should be checked. The lamp should not illuminate when the tires are properly inflated.

What does it mean if the lamp flashes on and off and then remains illuminated?
All TPMS installed on 2008 model year vehicles and beyond are required to detect and warn the driver when the system is not functioning properly (malfunction indicator). For some TPMS, a system malfunction is indicated by a flashing of the low tire pressure warning lamp for a period 60 to 90 seconds with the warning lamp remaining illuminated after the flash sequence.

The flashing sequence followed by continuous illumination of the warning lamp will repeat at each subsequent vehicle start-up until the malfunction is corrected. A vehicle dealer should be contacted for a system inspection.

Why does tire pressure change?

Many factors affect tire pressure including ambient temperature changes and tire damage, such as
punctures. Tire pressure drops about 1 psi for every 10 degrees F drop in ambient temperature. Additionally, tires lose as much as 1.5 psi per month as air escapes the tire and rim naturally.

What should be replaced when a sensor is removed from the rim?

The grommets around the base and nut of the sensor must be replaced every time the sensor is removed from the wheel. The material in seals has a “memory” of where it was placed and the amount of clamping force. When the old seal is taken of the rim, it is deformed and will not properly reseal if it retightened.  

Service packs provide the sealing components for each applicable sensor (clamp-in or snap-in) and can be replaced just as valve stems are today. Each time a clamp-in sensor is removed from the rim hole, the grommet, nut, nickel-plated core, cap and any other components supplied in the service pack should be replaced. Snap-in sensors should also have their rubber insert replaced each time the sensor is removed from the rim hole. The inserts should be replaced just as a standard valve stem is today.

What is the torque value required for the nut?
Typical torque values for the base nuts on a TPMS valve stem range from as low as 35 in.-lbs. of torque to as much as 80 in.-lbs. of torque. That’s quite a range. This does not mean that any torque value within this range is acceptable.

It means that the torque specifications for the base nut on one car might require 44 in.-lbs., another might require 62 in.-lbs. EXACTLY, another might specify 71 in.-lbs. EXACTLY, and so on. Don’t guess. Look up the torque specifications for the vehicle you are servicing to make sure you use the
correct torque.

Why should the nut be replaced every time a sensor is serviced?
The nut is made of a softer metal than the stem, so it will be damaged, and not the sensor, if it is overtightened. The material of choice is typically aluminum. If the nut is over tightened, it will develop hairline cracks.  

Will sealants damage a TPMS sensor?
Some tire manufacturers and TPMS sensor manufacturers do not support the use of tire sealants. The use of any liquid or tire sealant injected into tires equipped with tire pressure sensors is not recommended and may cause the tire pressure sensors to malfunction. One manufacturer of sealants states: “…sealant may come in contact with the sensor in a way that renders the sensor temporarily inoperable until it is properly cleaned, inspected and re-installed by a tire care professional.” But, it also states that the sealant is water based and will clean up with no adverse effects.

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