TPMS question

I have had my Prius for almost two years and never touched the reset button. I have run everything from recommended pressure to 42/40. And now have even put on a new set of tires and am running them just over the recommended pressure at 37/35. I have never had the warning light come on yet.

 

The "alert" pressure is 75% of the set pressure (when you press the set button). You only need to do the reset if you're changing the target pressure in the tires.

This would be if you're increasing the pressure from the factory pressure, or if you're rotating the tires (because the front two have a higher pressure).

If you're just refilling the tire to the previous set pressure, you don't need to reset anything.

 

Maybe your son read the Owner's Manual...

 

Uhh, you don't need to reset the system when you rotate the tires either. It doesn't care where the wheels are on the car. If -any- tire drops more than 25% in pressure from when you -last- set the TPMS, then you get a light. It can't sense where the tire is.

 

This brings up a side question: what does the TPMS use as the warning level? 75% of the average of the 4 sensors polled when reset? 75% of the lowest of the 4 at reset? Something else entirely?

 

well, each sensor sends its reading to the TPMS ECU- it will kick the warning light on when any of those 4 sensors reports a 25% loss. remember they have individual ID numbers and are separately identifiable.

if you collected the average, that would create a lot of problems when only one tire went flat.

 

Okay, but that also means that one should consider resetting when one rotates tires, because of the pressure differential front/rear.

 

That's what I meant -- if you keep 42/40 front/rear and rotate the tires back to front, you'll have 40/42. You should then add 2 pounds to the front and let 2 pounds out of the back, then reset the TPMS. The TPMS tracks each tire by the sensor serial number, not by its position on the car.

 

yes, any time you change the set pressure in your tires, you should reset the TPMS. if you are refilling them to the set pressure after a loss, say it gets cooler outside or something, you do not need to reset.