Changing TPMS Sensors

So what do you need to know before you change a tire on a TPMS equipped car?

1. How to avoid breaking the sensor.
2. The importance of torquing the valve core & sensor nut.
3. How to avoid interference that might block the signal.
4. What service parts you'll need to have on hand.
5. How to select a tire that will work with the TPMS system.

1. How to avoid breaking the sensor.


There are some different OE recommended methods, but the safest in my view is this.


1. Check the TPMS sensor signal to make sure it works before you begin.

2. Remove the valve stem core to relieve the pressure.

3. Remove the valve stem nut & push the TPMS sensor into the tire so it falls to the bottom.

4. Break the beads.

5. Remove the first bead. STOP.

6. Reach into the tire and get the sensor out.

7. Remove the second bead.

8. Reinstall the new sensor with a new grommet, retaining nut, using a torque wrench to torque it to the proper spec.

9. Rotate the turntable so the the valve is 270 degrees from the head on the tire machine. In other words, if the mounting head is at 12:00 the sensor should be at 3:00, assuming your tire machine's turntable rotates clockwise (most, if not all, do).

10. Begin mounting the tire. There is usually no trouble with the first bead. However, if the rim begins to move without the tire, as sometimes happens with low profile tires -- STOP! Back up and try again. If the tire is not fully mounted by the time the sensor comes around to the head, the head may snap the sensor off. With some wheels, head to sensor contact is not possible, but if you are not sure, it's better to avoid the possibility by making sure they never come close.

11. Seat the beads and install a valve core using the torque limiting valve core tool. If you lose the core that came with the TPMS sensor reseal kit, be sure the the replacement is nickel plated, not brass plated.



Is this more work than doing a non-TPMS tire? Yes. Is it fair to charge more. I think so. Besides, some TPMS sensor reseal kits, notably for the Honda/Acura TRW sensors, are $25 each! That's $100 for 4 tires compared to $4 for 4 tires worth of normal valve stems. There's no way to absorb an increase in cost like that. I'm sure there will be many shops that simply reuse grommets, or leave the sensors in place to come up with lower quotes, but I think that it will bite them in the end. Sooner or later they'll break enough sensors or have enough leak comebacks. The pressure is being monitored all the time; there's no way a customer is not going to notice a leak!

2. Torquing the valve core & stem nut


I mentioned the valve core torque and torquing the stem retaining nut in the tire replacement procedure. TPMS manufacturers are making a lot of noise about this, and I'm inclined to believe it's important. Every single nut and bolt on a car has a manufacturer's recommended torque value. However, with the exception of head bolts, spark plugs, and lug nuts, mechanics, for the most part, ignore these and use a combination of common sense and experience to tighten nuts and bolts. I'd rather not take any chances. A valve core torque tool is only $12, which is, lemme break out my calculator here, mmm, zero dollars more than a standard core tool. A 0-150 inch-pound torque wrench is a bit more, but most mechanics already own one. We bought on just for the tire room to encourage its use. I figure if it's the closest tool to the tire machine, it'll be what gets used.


3. Electrical interference


The TPMS sensor signal can reportedly be blocked by electrical interference. I've seen advice that non-stock valve caps can cause problems. I've also read that cell phones should not be used while registering or activating sensors. I don't really have enough experience to comment on whether interference is a real problem or not, but I suspect that it's not going to be a problem. There is so much electrical interference in all urban areas all the time, I can't imagine the engineers didn't consider it while designing TPMS systems. Here in the shop we have over 20 Bluetooth devices, 6 wireless access points, several 3G cell phones, a TIG welder, a bunch of 3 phase equipment, and lots of fluorescent lights. If a cell phone could really bring the whole thing crashing down, we'll be doomed for sure.


4. What parts do you need to stock.


We have TPMS sensor service kits on hand, since it's difficult to tell what kind of sensor the car has until the tire has been dismounted, and that's not the best time to begin ordering parts. The stem nuts all look pretty similar (at least for the cars we repair) and that is all that is visible from the outside the rim. The rubber sealing grommets and washers are all different each sensor type. For some sensors, like TRW, you'll need a whole metal valve stem to reseal. Others, like Schrader and Pacific, just come with a grommet, washer, Schrader valve, cap, and stem nut. Some stem nuts have a built in sealing surface, others do not. Some washers have a special shape, others are pretty standard. We have 4 kits that look identical from 2 feet away. You have to look really closely to see the differences. Unfortunately, there are not really any great application guides yet, but I'm sure there will be eventually. Meantime, we glued one of each type of kit to a piece of particle board for identification.


5. Selecting a tire that will work with the TPMS system.


Some cars *may* have a hard coded upper and lower tire pressure limit, which could potentially be an issue if you change tire models. For instance, the car may have originally come with a 185/65R15 86H, and a recommended pressure of 30 PSI. On this OE installed tire, 30 PSI would be adequate to maintain the 86 load rating. However, if you replaced the tire with a different model (same size & load rating), 30 PSI may not be an adequate pressure. Tire manufacturers usually list the minimum pressure to meet the stated load rating in their catalogs. If a tire with a load rating of 86 at 35 PSI is installed on a car that requires a tire with an 86 load rating and a tire placard that says 30 PSI, the tire still must be inflated to at least 35 PSI to be safe, wear properly, and achieve good fuel economy. I have heard that some cars have hard coded upper and lower limits tire pressure limits (but haven't actually seen one yet). On a car like this, it would be very important to verify any replacement tire selected would not only meet the vehicle manufacturer's required load rating, but would also do so at the pressure listed on the placard.


Can't you guys just disable that annoying TPMS light? I don't want to pay to fix a system I don't even want!
No. It is illegal to disable the TPMS light per FMVSS 138. We're not willing to pay fines or go to jail to reduce your annoyance. Are you required to fix the TPMS light? No, you're not. Could we install 24" non-TPMS rims with 35 series tires on your Corolla. Absolutely not, but not because it's illegal, it would just look really silly. The law says your warning system must not be disabled, but apparently a working warning light is considered "working". Goofy rims without TPMS are legal, so long as an auto repair shop does not disable your TPMS light. Can you disable your own TPMS light? It's fine with me. I won't tell anybody.
What should you do when the TPMS light is on?

There are two types of TPMS lights for Honda & Acura cars.

One type indicates low tire pressure, and requires nothing more than resetting the tire pressure. You should ask your customer if they have already tried this before signing them in. If they haven't, explain how the system works & send them on their way. You can set their tire pressures for them, but bear in mind that if they just drove in, you won't be setting pressures cold. If the customer says they've already tried setting their tire pressure, and they sound like they have been doing it correctly, sign them in for inspection.

The other type of TPMS warning light indicates a problem with the TPMS system. There's no need to check tire pressures. Go ahead and sign the customer in for diagnosis.


(above) Just fill the tires & drive for a while. If the light goes out, you're done!

(above) The TPMS system needs diagnosis.

Images courtesy of Honda

Toyota just uses one light to indicate low tire pressure & system problems.

A steady light indicates low tire pressure. You should advise the customer to fill their tires to the desired pressure cold, then use the TPMS button to reset the system (more on that below).

A flashing light indicates a problem with the system, and the customer should be signed in without a tire TPMS lecture.


Image courtesy of Toyota
The Nissan TPMS warning light works the same as Toyota. A solid light means low tire pressure. A flashing light indicates a TPMS system fault