Can you replace just the valve stem on the TPMS?

If it is a TOYOTA OEM TPMS ( I think made by Pacific, IIRC), then the answer is NO. The TPMS sensor and the valve stem can not be separated. If it is aftermarket TPMS like Autel MX sensor, then YES, they can be separated and just valve stem can be replaced.

One shown in the photo is the Autel MX sensor with a Press-on valve stem. You don't even need a screwdriver to detach the valve stem.

 

You should probably replace the entire set; since the batteries on them are more than half way gone anyway. They were $65 USD for a set on amazon.

 

Yeah, if you are using an external TPMS sensor, there is no point in having internal TPMS sensors too. In the US, by law, tire shops can not replace working TPMS sensors with a standard valve on a car. But if I just bring a tire, they will switch it.

Why is the price so high? Does $160/wheel include installation? It was not for Prius, but the last OEM sensors I bought for Honda (also made by Pacific, I think), I paid less than $10/pc from eBay.
toyota tpms | eBay

You can also go with aftermarket TPMS, like Autel MX, but then you will need it to be programmed. Where I live, it cost ~$50/wheel for aftermarket non-programmable TPMS sensor parts and installation at a tire shop. They don't usually stock OEM sensors. If I take my car to a dealer to install an OEM sensor, they charge $100-$150/wheel.

I had no TPMS on my winter wheels for 3+ years and used external TPMS sensors. But I recently had a shop install the Autel MX sensors which came with the TPMS tool I bought and cloned IDs from summer wheels into my winter wheels. The cost of TPMS installation is the same as installing a new tire. I was going to wait till the next set of tires, but I am not driving much nowadays, If I waited for the next set of tires, it will be several more years.

 

I was wonder if you had annual inspections that would compromise your plan on replacing it with standard valve stems.
On my 2021 LE, which I think is the equivalent to your excel - the tire pressures show up on the Toyota app only. You may try your Entune app if your paying for connectivity. If this was me; I'd take it to a large independent tire shop to get it replaced and cloned.
I used to use a cheap knock-off set of these:

on my old 2012 Prius C and my other car w/o TPMS. Just a quick walk around the car for a quick visual check. It was made of molded cheap rubber/plastic. When I replaced the tires, I specifically asked the tire mechanics to use the shortest valve stem the had, so these things don't protrude out so far.

 

I agree with all of your points. I have gone through the same thought process and experience with my own cars but with slightly different outcomes.

1. The price of TPMS installation: I see that your $160/wheel is including installation and OEM TPMS. That cost is similar (although on the higher end) to what I found in the US Toyota dealer replacing OEM TPMS. And your local garage job $75 for an aftermarket TPMS is again similar (although on the higher end) to what I found in the US at an independent shop. Most of the cost comes from the actual dismounting and remounting and balancing tires. In the US, the cost of installation (or replacement) of an internal TPMS sensor is identical to the cost of installation of a new tire. If you can provide TPMS sensors purchased online at the time you must purchase new tires, then you can save a lot. As pointed out, the online purchase of OEM TPMS sensors is ~$10 each in the US.
2. Failing annual inspection due to non-functioning internal TPSM: I thought similar issues with my first internal TPMS equipped vehicle, thinking I must have functional TPMS to pass the annual inspection. The law maybe different in UK, but at least in the US, most of the states that require annual inspection do not require the functional TPMS. Only a few states actually require the functional TPMS in order to pass the inspection. My state does not require it although at first, I thought it did. So, for my winter wheels without TPMS sensors inside (meaning TPMS warning light is lit on the dash all the time) was OK.
3. Problem with external TPMS: Yes, I have had the external TPMS corroding onto the metal valve stem before. BTW, this can also happen with decorative metal valve caps. I destroyed one set of external TPMS after a single winter due to this galvanic corrosion. The simple solution I found effective in preventing this galvanic corrosion was to apply the thread of the TPMS sensor cap with anti-corrosion spray. I did that once when I changed a tire in winter and whenever I had to remove the sensor cap to top off the air. Never had the galvanic corrosion again. My problem with the external TPMS was more of the quality and durability of the sensors. With our very harsh winter and road salt, I often had the external sensor not lasting more than 1 year or so. And when one sensor fails, the entire set including the display unit on the dash had to be replaced. Granted, it was only ~$30 for an entire set at Amazon, still, it was becoming more of an annoyance. Thus the recent effort to install internal TPMS sensors on the winter wheels.
4. Problem with internal TPMS: I understand where you are coming from. The Pruis's dumb TPMS has very little utility in topping off the tire or knowing how high or how low the tire pressures are. I have been using my TPMS tool to check the tire pressure off from the internal TPMS sensor signal. This makes it much easier than using a manual tire pressure gauge. I also have used an OBDII adaptor and an APP Tire Assistant. It can display ECU data from the internal TPMS sensors for the sensor ID, pressure, temperature. The caveat is that it is available only in the Android App store and it can not be used for getting live data while driving similar to using Techstream. Also, the TPMS data do not indicate the location of the four corners unless you specifically change the ECU program to correspond to the correct location on the diagram. But the worst part is that for an unknown reason, the Psi value is somewhat off from the live data read off from the TPMS sensor using the TPMS trigger/read tool. I think this is because the stored data in ECU is somewhat older than the live data the sensor when the sensor is triggered by the TPMS tool.
   
5. Other methods for monitoring TPMS: I have read that Carista App also has the TPMS information capability but did not find that to be the case at least not on my app when I used the app with a free trial subscription specific to PP. For Prius, the only way I know how to extract the live TPMS data off from ECU via OBDII port while driving is using ScanGauge II with X-gauge program PID for TPMS. But just for live tire pressure info, not many people are willing to pay ~$150. I did, but after finding out how tedious using X-gauge program PID on the tiny antiquated display of ScanGauge II was, I totally dismissed using it.

Here is the screengrab of the TPMS Tool reading off of the internal sensors and by the Tire Assistant APP via OBDII connection read 1 min apart. Note that the location of the sensor on the Tire Assistant App is wrong and the Psi reading is not the same as what was reported by the TPMS tool.

 

I am a little confused by the discussion about getting TPMS pressure info on the Prime. I just use the Carista app with their OBD-II dongle. The tire pressures are on a TPMS screen under the service menu. It lists the ID and pressure for each tire (it is up to you to figure out which ID is on which tire). This functionality is part of the free features that does not require a subscription.

Are people talking about something else, or what? Sorry if I am off base here.

 

That's funny. When I used the Carista App on my previous 2020 PP during the free subscription period to customize it, I specifically looked for the TPMS function but could not find it. I have read in another thread that TPMS functionality was added for PP at some point in updated app, but that was not available when I was looking for it. I will check again with my current 2021 PP. If it does display TPMS info for you, can you display it while driving? An app like Tire Assistant I mentioned above does not allow live data streaming when the car goes into the READY mode for safety reasons. As I understand it same is true for the TechStream.

 

When I got Carista around three years ago to do the backup beep fix on my 2017 Advanced, I believe that the TPMS menu was there at that time. See https://blog.caristaapp.com/easy-to-use-tpms-tools-for-toyota-from-carista-c1811bb50c38 dated September 21, 2018. I think that reading the pressures is free, but if you want to register new sensors, that requires a subscription. I think that the app does not support while-you-are-driving live displays. The TPMS stuff is under the "Advanced Service" menu.

 

Yeah, that was my understanding as well. But when I played with Carista to customize my 2020 PP, I did not find the TPMS info on my phone APP. I might have simply overlooked it. If it is a free part of the App, I can check it again later. In any case, thank you for confirming that it does not let you monitor the tire pressure while driving. I think, for safety reasons, that functionality is more important than the ability to check the TPMS sensor data when you are parked.