TPMS Sensors: Batteries, Relearns and New Tires

What a TPMS sensor is, and why you have one

Passenger cars, SUVs, pickups and vans built for the US from September 1, 2007 onward have a tire pressure monitoring system. The federal rule, FMVSS No. 138, covers passenger cars, multipurpose vehicles, trucks and buses with a gross vehicle weight rating of 10,000 lb or less, except those with dual rear wheels.

The rule sets what the system must do: light a warning no more than 20 minutes after a tire drops to 25 percent or more below the vehicle maker's recommended cold pressure, and light a malfunction warning when the system itself stops working. Our guide to the TPMS light covers what the dash is telling you. This one is about the hardware behind it.

Direct vs indirect TPMS

There are two ways a car can watch your tires.

Pirelli describes direct TPMS as a pressure sensor attached to the back of each tire's valve, and indirect TPMS as using existing sensors, such as ABS and wheel speed sensors, with software inferring the pressure. Continental explains the indirect logic: a flat tire rotates faster than the others, and the system detects and flags it.

Your owner's manual says which system your car uses. If your dash shows a separate pressure reading for each tire, that points to a direct system.

Sensor batteries: the part that wears out

A direct TPMS sensor is a small radio transmitter with its own battery, sealed inside the wheel. That battery is the usual reason a sensor fails.

Pirelli puts it plainly: TPMS sensors most often need to be replaced because their batteries have reached the end of their 5- to 10-year lifespan. It adds that most sensor models have built-in, non-replaceable batteries, so the only solution is to replace the whole sensor.

There's a knock-on effect. Continental notes that you don't always need to replace all four when one fails, but the other sensors are likely close to failing too, due to old batteries. Sensors from the same car usually have the same birthday.

What a dying sensor looks like from the driver's seat: the TPMS light flashes at startup and then stays on, the malfunction pattern the federal rule requires. Pick that pattern on the explainer below to see what it means:

Relearns: telling the car where each sensor is

Each direct sensor broadcasts its own ID. The car needs to know which ID belongs to which corner, and which IDs are on the car at all. Tire Review defines a TPMS relearn as the process of programming new sensor IDs or repositioning existing IDs in the vehicle control module.

When a relearn or reset can come up:

• After a rotation, when sensors change corners.
• After a new sensor is fitted.
• After a wheel swap, such as a second set of wheels.

How it's done varies by car. Continental notes the sensors recalibrate on their own in many cases, but sometimes you need to manually reset them, or replace them if the light stays on. Pirelli's advice is that TPMS resets should be done by a tire professional. Your owner's manual lists your car's procedure. Tesla owners can see how that maker handles it in our Tesla rotation, alignment and TPMS guide.

What happens to the sensors when you get new tires

New tires don't automatically mean new sensors. A working sensor is moved over to the new tire on the same wheel. What does change:

1. The seals and valve parts. Per Tire Review, USTMA, TIA and many vehicle OEMs all say that every time a tire is taken off the wheel, the sensor's wear items should be replaced. The reason given: rubber seals break down over time and are prone to leaking if the sensor is moved or twisted during dismounting and mounting. These parts come as a TPMS service kit.
2. A check that the system still works. FMVSS No. 138 requires the owner's manual to tell you to check the TPMS malfunction telltale after replacing one or more tires or wheels, so the replacement tires and wheels allow the TPMS to continue to function properly. The rule notes that replacement tires or wheels can prevent the system from working.
3. A conversation about age. If your sensors are in the 5- to 10-year range Pirelli describes, it can make sense to replace them while the tires are off anyway, rather than dismounting a new tire later.

TPMS is a backup, not a gauge

The warning comes on at 25 percent low. A tire can be well under the placard pressure with the light still off. NHTSA's advice stands no matter which system you have: check all four tires, and the spare, with a gauge at least once a month, cold. Our guide to checking tire pressure walks through it.

TPMS at Extreme Tires

Every tire installation from Extreme Tires includes valve stem replacement and a TPMS reset where the car has one. Its TPMS service covers:

• sensor scan and battery health check
• sensor replacement where needed
• relearn and programming to your vehicle
• pressure set to placard spec

It's done at the Sunrise shop or from the mobile van at your home or office across Miami-Dade, Broward and Palm Beach. Buying tires here? Tires ship free to the 48 contiguous states and DC, and you can book installation or a mobile visit when you order. Mention a TPMS light when you book; the van carries a TPMS programmer.

Quick reference