I wish I could figure out how to initialize the TPMS...

If this is a 2016 or newer you do it thru the menus accesed by the steering wheel buttons. Its under the maintenance menu.

 

Yep, tpms is reset in the menu display and not on the head unit with an app. Scroll to the right using the steering wheel control. When you get to maintenance menu you can select tpms reset, or oil maintenance. It should be in your manual. Good luck, hope this helps.

 

This is because you adjusted tire pressures, want to set a new baseline?

Dumb question I know, that's my department.

 

Third gen had a dedicated button for the reset. It was under dash, in vicinity of OBD port. Yeah I know, not helpful, just a tirade, lol.

 

From the 2016 manual:

 

Yeah. Mine were set at 32 psi by the dealer for my 150 mile drive home

 

I assume initialization sets the known pressure for each tire to the current value. So for example if I inflate to 50 PSI and then do an init, the low tire light will come on when the pressure falls by 20%. Correct?

 

That is correct.

 

Wow, 20% is a big variation! About 7 psi at Toyota recommended pressures! That's a LOT more than I expected. I assumed it would be more like 10%.

Where is this percentage documented?

Am surprised that the car doesn't have the ability to display the actual pressures. That would be a lot easier than having to check using an air line or pressure guage.

Is there any easy way to get at this info?

On the other hand, the latest generation of ABS sensor based indirect TPMS monitoring seems a better option in view of not needing any sensors on the tyre. No problem if you use gunk to repair the tyre, of needing an expensive sensor replacement!

They have these on the RAV4 according to what I read.

Posted via the PriusChat mobile app.

 

A 4+ PSI change will occur just between a cold start and 20 minutes of driving. When the tire gets hot, the pressures come up. If it was set to 10%, the light would be on 100% of your drives over 20 minutes. If you set it to be the hot pressure, it will come on every morning when it's cold. Set it cold, it will come on after 20 minutes of driving until it cools down. Can't win.

Also you get about 4.6PSI difference every 10K feet above sea level. Where I live, that means I lose and gain at least 1PSI just driving between home and the main city with the elevation changes and another 3+ PSI driving to lots of places within 2 hours from here. And another 1.5PSI for each 10C temperature change.

Add to that, most TPMS systems including the Densos are 3% accurate over the usable range of conditions.

20% is very reasonable.

I've heard between 20% and 25%. I don't see it in the manual or tech service manual. So I don't know

All this info is reported on the CANBus and is available to any CAN reader. Even a phone with a bluetooth OBDII port reader can give you the information if you want. Toyota reserves displaying this information to the Lexus line of vehicles and some of the SUVs. The info is still there though, you just don't get a pretty picture of each wheel with pressures. And of course the picture if displayed would be inaccurate if you did a tire rotation and didn't change the ID values with a TechStream.

Not sure of the latest gen, but the previous generations that used that method had a fundamental limitation of only being able to report an outlier. If all your tires were crap, it would register OK. If 2 were bad, it would have a generic error. It only works when 1 tire is rotating differently than the rest (baseline). Having actual digital sensors is a much better solution, even if it costs you an additional $35 per tire every 10-15 years.

 

Thanks. Interesting.

I read that the latest gen of indirect TPMS gets round the problems that you refer to. All it has to do is remember the data for each wheel when you initialize it, and then compare with that stored data rather than with the other wheels. Ok, that's simplistic, but perhaps broadly true.

AFAIK the TPMS only reports pressure below threshold and not above it. See a recent post from Bob Wilson in a different thread, who says he inflates his tyres to 10 psi over spec, and then the TPMS alerts when they get below actual spec.

In my case, I just checked my pressures and found one to be 29 when I had set the TPMS at 36. No alert from the TPMS. Just inside of 20% but more than enough to affect tyre wear and mpg negatively. So to me, the TPMS seems of very limited value most of the time, compared with what I expected or hoped.

Posted via the PriusChat mobile app.

 

How on earth did we manage before tpms was invented? Strange that the motoring population survived unscarred psychologically at all!

 

There are some that would argue that many, possibly a majority of society is psychologically scarred,

 

Down, Harvey!

 

Yes but not physically possible to detect what the problem is. It is a trick that only works in certain scenarios and there is good reason to use it in some cases. But it is inferior to an actual sensor in every way except cost and complexity.

TPMS does report when pressure is too high, something around 70+ PSI. It also reports when too low, just waaaaay too low. What you mention is the standard way to make the TPMS sensor work for you. Work backwards from what you want. If you want the TPMS lights to go on at 38PSI for example, then inflate your tires to 47.5PSI or so, and press the TPMS calibrate button or the soft-button on the Gen-4. That's why there is the button and Toyota doesn't just set it at the door PSI value. Remember the car knows the exact PSI of the tire in psuedo-real-time down to a tenth of a unit. It would be really easy (and cheap) for Toyota to just say, the lower limit is 28PSI, done. But instead they give you a knob to turn to set it to what you want. The only limitation is that it has to be above about 15PSI and below roughly 70 PSI and the sensors will alarm if it drops to 20% less than whatever value you want.

When you say you had the TPMS "set to 36", does that mean you inflated to 36 PSI and calibrated, or set to 45 PSI and press calibrate? Because if you inflated to 36 PSI and press calibrate, then you are within 20%. It did as it should. In your case if your temperature and elevation are relatively stable, then you just again set them to where you WANT them. If you want your tires to alarm at 32 PSI and roll with 36 PSI normally, then it is really simple.

(1) Inflate tires to 40 PSI
(2) Wait 5 minutes
(3) Do TPMS calibration and wait for it to finish (usually less than 2 minutes)
(4) Deflate tires to 36 PSI
(5) Profit.

What you've done is set your region of OK tire pressures to be 32 PSI (80% of 40 PSI) to 70 PSI. You can drive at 36 PSI all day long and it will let you know when outside the region. Exactly what you want, so that's good.

Checking your vehicle was more routine because you expected something to be wrong. How often do you see someone at the gas pump walking their car? Checking tires, popping the hood checking fluids, etc. That was just done all the time because without constant maintenance the car just wouldn't work. Now the cars are reliable enough that we wait until something literally explodes before we take it in for service. Read most of the threads around here and you find threads where the master warning light came on and the check engine light came on and they continued driving it for weeks because they didn't have time to figure it out or didn't know it was that serious. When the car dies and leaves you stranded, then it is serious enough to be cared for, otherwise the car just operates.

 

Long live the hypothetical question! Seriously, your answer is spot on.