TPMS Sensors

How do programmable aftermarket TPMS sensors work?

Short answer: A programmable sensor is a blank that your TPMS tool loads with the right protocol for the vehicle, or a copy of the original sensor's ID, so one part number covers many vehicles.

Original sensors are made for specific vehicles. Programmable aftermarket sensors carry multiple protocols and are configured with a TPMS tool for the vehicle you are working on. That lets a shop stock a few sensor types instead of hundreds of part numbers.

There are usually two ways to program them. Create a new sensor gives it a fresh ID, which then requires a relearn to the vehicle. Copy or clone reads the original sensor's ID and writes it to the new sensor, so the vehicle recognizes it without a relearn on many models.

Confirm sensor coverage for the vehicle with the sensor maker's lookup and your tool, check frequency, and follow the torque values for the valve nut or core. Replace valve cores, seals and caps with service kits when you reuse a sensor.

What are TPMS relearn procedures?

Short answer: A relearn teaches the vehicle the IDs and positions of its tire sensors, done automatically while driving, through a stationary sequence with a TPMS tool, or by writing IDs through the OBD port.

When you install new sensors or rotate tires on some vehicles, the vehicle needs to learn which sensor IDs it should listen to and, on some systems, which wheel position each is on. There are three main methods.

Auto relearn: the vehicle learns the new IDs while driving for a set time and speed. Stationary or manual relearn: you put the vehicle in learn mode, often through a sequence of key, button or brake steps, then trigger each sensor in order with a TPMS tool. OBD relearn: the TPMS tool reads the sensor IDs and writes them to the vehicle's module through the diagnostic port.

Your TPMS tool or service information shows the correct procedure for each vehicle. Following it exactly avoids a TPMS light coming back after the customer leaves.

Can I replace the battery in a TPMS sensor?

Short answer: Most TPMS sensors use a sealed battery that cannot be replaced, so when the battery runs down the whole sensor is replaced; a TPMS tool can show battery status before it fails.

TPMS sensors sit inside the wheel and transmit for years on a small battery that is sealed into the housing to resist moisture and vibration. Once it is depleted, the sensor stops transmitting and the system sets a fault.

Because sensors on the same vehicle are usually the same age, when one fails from a low battery the others may not be far behind. Many shops check all sensors with a TPMS tool, which often reports battery status, and discuss replacing them as a set, especially when tires are being replaced anyway.

Replacement can use an OE sensor or a programmable aftermarket sensor set up for the vehicle with a TPMS tool. Replace the valve core, seal and nut with a service kit, and torque the nut to the sensor maker's specification. Deflate the tire fully and follow tire machine safety procedures before breaking the bead.

Why do TPMS valve stems corrode, and how do I prevent it?

Short answer: Aluminum clamp-in stems can corrode when moisture and road salt reach them or when mismatched valve cores are used; using the correct service kit and a fresh cap at each tire service reduces failures.

Clamp-in TPMS stems are often aluminum. Corrosion builds up where the stem meets the nut, core and cap, especially in salted climates. A seized core or nut can snap the stem during service, and a cracked stem can leak.

Use the valve core type the sensor maker specifies, since mixing metals encourages corrosion, and replace the core, grommet, washer and nut with a service kit whenever the tire is dismounted. Install a sealing cap of the correct type. Torque the nut to the maker's specification; overtightening cracks stems and undertightening causes leaks.

Inspect stems at every rotation and tire change. Deflate the tire before working on the stem, and wear safety glasses, since a core can eject under pressure.

What is the difference between 315 MHz and 433 MHz TPMS sensors?

Short answer: They are the two radio frequencies TPMS sensors commonly transmit on; the vehicle's receiver listens on one, so a replacement sensor must match the frequency the vehicle uses.

The TPMS module receives radio signals from each sensor. Vehicles are built to receive on a particular frequency, commonly 315 MHz or 433 MHz depending on the maker and market. A sensor on the wrong frequency will not be heard.

Programmable aftermarket sensors often come in versions for each frequency, or in dual-frequency versions, and are programmed with the protocol for the specific vehicle. The TPMS tool's vehicle lookup tells you which sensor and protocol to use. Vehicles imported from another market may differ from local versions, so confirm against the original sensor or service information.

Stocking the right mix of programmable sensors lets a shop cover many vehicles from a small inventory. Follow tire machine safety procedures and deflate the tire before removing a sensor.

How do I install a TPMS sensor correctly?

Short answer: Install the sensor with new service parts, torque the nut or screw to the sensor maker's specification, position it correctly in the wheel, and program or relearn it before releasing the vehicle.

TPMS sensors have specific installation requirements. Replace grommets, valve cores and nuts as recommended. Overtightening can crack sensors or damage valve stems.

Use a torque tool for the valve nut and core as the maker specifies. During tire mounting, position the bead breaker and tire machine away from the sensor to avoid damage.

After installation, program the sensor if needed and perform the relearn procedure. Wear safety glasses and follow tire safety rules when inflating, using a cage or clip-on chuck where appropriate.

What does cloning a TPMS sensor mean?

Short answer: Cloning copies the ID of the old sensor into a programmable replacement so the vehicle recognizes it without a relearn, which can save time when the old sensor can still be read.

Programmable sensors can be set with a new ID or a copy of the original sensor's ID. Cloning reads the old sensor and writes its ID to the new one.

Cloning only works if the old sensor can be read. Some vehicles still need a relearn after cloning.

Cloning is handy for tire shops when a customer cannot wait for a full relearn, but if the original sensor has failed and cannot be read, create a new ID and perform the relearn instead.

Check the sensor maker's instructions and the vehicle's procedure. Verify all sensors read correctly before releasing the vehicle, and follow tire safety precautions.

Do TPMS sensors need special care during tire mounting?

Short answer: Yes; position the bead breaker and mounting head away from the sensor, follow the tire machine's instructions, and inspect sensors and valve parts each time the tire is serviced.

TPMS sensors are mounted inside the wheel and can be damaged by the bead breaker or mounting tools. Start mounting and demounting with the sensor in the position the tire machine maker recommends.

Inspect the valve stem, nut and seal each time, replacing service parts as needed. Torque valve nuts to the sensor maker's specification.

Damaged sensors set warning lights and lead to customer comebacks. Taking an extra moment to position the sensor correctly saves time and money.

Wear safety glasses, keep hands clear of the machine, and use a safety cage when inflating.

Should I replace TPMS sensors when I replace tires?

Short answer: Not always, but a tire change is a good time to check sensor condition and battery status and to replace worn service parts, since the tire is already off the wheel.

TPMS sensors often last for years, so they do not need replacement with every set of tires. However, a tire change is the easiest time to service them because the tire is already off.

Check each sensor with a TPMS tool for a reading and battery status. Replace seals, nuts and valve cores as recommended, and consider replacing older sensors that are near the end of their battery life.

Explain the options to the customer and record the results. Torque valve nuts to the sensor maker's specification, wear safety glasses when inflating, and perform any required relearn after service.