Tire Pressure and TPMS

I believe from what I have seen on posts the Threshold is 8 PSI, and that is what activates the TPMS. I just took delivery of my 2010 Model V on Friday and the TPMS lit up today?? I checked the tire pressures and they are at 38/36. So I don't know why it's lit, since it seems to be close enough to the set pressures. I am going to call the dealer Monday to see if they can take a look at it.

I have the 17" wheels with low profile Bridgestones so I am not familiar with them enough for the Tire pressue.

Let me know what you find out.

 

Did you set the TPMS after inflating the tires to your desired pressure after taking delivery? The owner's manual says you need to initialize the system when you first take delivery. There's a button under the dash by the steering column, which you hold until the light flashes a few times on the dash and then stops flashing.

Even with TPMS in cars, I make it a habit to check the tires once a month

 

If the Gen III TPMS is the same as the Gen II's, then the TPMS warning light will turn on when the psi of one of the four tires drops 25% below what the psi is set for.

For instance, if the TPMS is set for 40 psi, then the TPMS warning light will go on when one of the tires drops to 30 psi.

 

The button is farthur underneath than on the GenII.
Look under the dash where your left leg goes and you will see the computer hookup connector "its white".. about 2 inches to the right is the reset button.

After setting your new tire pressures, while the car is on... hold that button down and you will see the tire inflate button light up in the far right of your forward dash panel... once it flashes "3" times, you can let go... then its reset.

 

The manual also says the car must remain in Ready (hybrid off) for several minutes to complete initialization. The get-ready sheet that was included in the manual download on another site actually tells the service tech to leave it on for 5 minutes. I read into that that you can't drive for those 5 minutes. I've had other cars with TPMS, didn't need to let it sit, but the Prius manual does call for it.

 

If that is the case then it seems like the best thing to do is take the tire pressure you want, divide by 0.75 then subtract 1 (if you ant a 1 psi buffer). Whatever that number comes out to be would be the number to inflate your tire to. After that one can then set the TPMS. Once set, reduce the tire pressure to the desired pressure.

In my case for example, I want to run 42/40.
(42/0.75) - 1 = 55
(40/0.75) - 1 = 52

So I increase the tires to 55 and 52 psi respectively then set the TPMS. After that, the system would warn me if my tires drop below 41 or 39 psi respectively. Saves me the trouble of checking and keeps me running at/near the psi I want. Assuming it will warn when the pressure drops 25% below.

 

That assumption does not appear to be correct for the GenIII TPMS system. Based on a printout of information from the Techstream device that I weaseled out of my dealer, the difference is either a percentage around 20% or it is a static number in the vicinity of 8psi.

 

Thats how it does work... whatever you set your psi to and then calibrate, it warns you so you can maintain that level.