1. Every time a stem-mounted TPMS sensor is removed from a rim, it must be serviced — no ifs, ands or buts. This goes for sensors that are six months old to six years old. Do not reuse seals or stems.
2. Always use a new kit. The typical kit includes a nut, valve core, grommets and valve cap. Each component has a specific function and lifespan that is not only determined by time, but what happens when it is installed.
3. Buy an assortment of TPMS sensor service kits. If your shop even sells a few tires a week, your shop should stock an assortment of service kits. Most tire product suppliers have cabinets filled with the kits you will need most. Not having the parts to service sensors might leave a car stuck in a bay that could be used for other repairs.
4. Never reuse the nut. TPMS nuts are designed in anodized aluminum to eliminate the contact of two dissimilar metals that would create galvanic corrosion and material deterioration. The nut has a bonded lubricant to help provide the proper torque required for seating a new grommet, in addition to the engineered advantages. If a nut is reused, the anodized surface may be scratched away and corrosion may occur between the sensor, wheel and stem. The nut may then be impossible to torque to the correct specifications or remove due to corrosion on the threads.
5. Never reuse the seals/grommets. On the sensor and nut, two grommets seal the sensor and nut to the wheel. Grommets conform to the mating surface of the rim. The instant the nut is torqued, it starts to take on the shape of the surfaces it is sealing against. This memory cannot be erased. If the seal is reused, it could cause a slow leak.
6. Always use a torque wrench. The torque specifications are measured in inch-pounds and not foot-pounds for a reason. As stated in Nos. 4 and 5, the nut and grommet seals are one-use items. The nuts are made of aluminum and will strip. The hollow stems can take only so much abuse before they break.
7. A leak will not be eliminated by tightening the nut more. The sealing grommets are engineered to work at a specific torque. Any torque above the specified value will cause the seal to leak, and extra force may damage the nut and stem or fracture the sensor body.
8. Never reuse the valve stem. Replacing the valve stem core on TPMS sensors prevents leaks. The elastomeric rubber and plastics degrade over time due to heat. The valve stem is subjected to heat from both the brakes and road. A torque-calibrated driver should be used to tighten the valve core.
9. Always use the valve core that is in the kit. A TPMS valve core is nickel-plated and prevents galvanic corrosion and ensures the integrity of the primary seal. To prevent galvanic corrosion, never use a brass valve core with an aluminum TPMS sensor. Instead, always use a nickel-plated valve core with an aluminum TPMS sensor. If the wrong valve core is used, accelerated galvanic corrosion could result in the core becoming “frozen” and seized, stuck in the stem and unable to be removed. TPMS valve cores also have special Teflon coating that helps seat and seal the stem.
10. Set the correct tire pressure. Seasonal temperature change can dramatically alter tire pressure, which can cause the tire pressure warning lamp to illuminate. “Cold” tire pressure, as shown on a vehicle’s tire pressure label, is the pressure in a tire that has been parked outdoors and not been driven in four hours. Tire pressure drops about 1 psi for every 10º F drop in ambient temperature. Additionally, air escapes the tire and rim naturally, causing as much as a 1.5 psi drop per month.
11. Take extra care when mounting and dismounting tires. When you are using a tire changer, always be aware of the TPMS sensor location and avoid all possible contact with shovels, bead breakers and tire irons. Some Ford sensors also are mounted on the rim 180º from the valve stem.