TPMS alarm went off...

[summerwind]

Bad news....the TPMS alarm went off.

Good news...I now know how to lower the spare and add air.

[TrailDust]

You're supposed to fill it before the warning goes off. For that you get one of these....

[05Moose]

(I take back what I said about this side being tame...oh wait, you don't count!)

Why bother lowering it...just hit the reset button to silence it!

[summerwind]

The reset will not work as long as the spare is low in pressure.
The weather was in the 20's and the tire psi dropped to 26 psi.

Increased the pressure to spec and held the reset button in for 3 seconds and things are back to normal

If I ate TrailDust's dust offroad I would drop the spare before hitting the back country but being a city boy AAA works for me

[05Moose]

Originally Posted by summerwind

The reset will not work as long as the spare is low in pressure.

Now you got me wondering...is the reset button in these different than the Tacoma? In the Tacoma, the reset button sets the pressure to the current levels. Then the TPMS light comes on when one of the tires drops 2-3 psi below where they were set to (when the button was pressed).

To clear the light, you don't actually hit the reset button. Putting air back in the tires clears it automatically the next time it does its check. So in the case of the Tacoma, you can hit the reset button when a tire is low to clear it because the reset button just sets the new "normal" level of pressure. Of course, you don't really want to do this because then you've set it to allow the tire to be too low. But the reset is a handy feature if you want to keep your pressure at say 33 psi allowing you to manually set the TPMS to consider 33 normal. Then if it drops down to around 30 psi, it tells you.

But I hadn't actually considered what would happen trying to set it to a new level if one tire was lower than the other 4. Maybe it doesn't work? One of us is going to learn something from this thread even if you didn't intend it to.

[Thunderchief]

Originally Posted by summerwind

Bad news....the TPMS alarm went off.

Good news...I now know how to lower the spare and add air.

Wish I had a a spare tire option instead of cargo compartment in the back. I rather have had a spare tire under the floorboards. I to had to learn to lower the spare when my TPMS went off.

[summerwind]

Hybrid models don't have a reset button and display the individual tire pressures on the MFD.

Non Hybrids have a reset button and the following link tells you how to find the button

http://mojavetrail.webng.com/TPMSreset.pdf

I don't remember but I think it will reset the light automatically after you start and stop the HL over a period of time.

[kkovak]

I thought I'd share some info on how far your tire pressure will drop as the temperature gets colder. To calculate the change in pressure (dP):

dP = (Pwarm+14.7)*((Twarm - Tcold)/(Twarm+459.7))

So if you are at sea level (14.7 psia) and you set your tire pressure in your warm (70°F) garage, and left your car outside where it is 20°F, assuming your tires were at the recommended 30 psig when warm; the pressure would drop ~4.2 psi down to 25.8 psig. Which I understand to be below the alarm set point for the TPMS (26 psig?).

Ken

[05Moose]

Originally Posted by kkovak

I thought I'd share some info on how far your tire pressure will drop as the temperature gets colder. To calculate the change in pressure (dP):

dP = (Pwarm+14.7)*((Twarm - Tcold)/(Twarm+459.7))

So if you are at sea level (14.7 psia) and you set your tire pressure in your warm (70°F) garage, and left your car outside where it is 20°F, assuming your tires were at the recommended 30 psig when warm; the pressure would drop ~4.2 psi down to 25.8 psig. Which I understand to be below the alarm set point for the TPMS (26 psig?).

Ken

The alarm set point is wherever you set it. That's what the reset button does. From what I've read and been told, the system will trigger when the tires are 2-3 psi below wherever you set them. I've seen it trigger when it's 2 psi below the set point on our previous 05 HL (door placard said 28, but I set it to 30 psi and it triggered when they dropped down to 28 psi), but that system uses passive TPMS while the 2nd Gen HL uses Direct TPMS. I assume it uses the same variance, so it should be 2-3 psi.

[AXMACD]

there's a tpms alarm?

[Robert1820]

Hey kkovak, thanks for posting that formula. I work in the service and tire bizz and when this subject comes up, they use a "rule of thumb" factor of 1psi/10deg.F. This ignores the need to use absolute pressure and temperature to accurately calculate.

[summerwind]

Originally Posted by AXMACD

there's a tpms alarm?

We are talking about the TPMS indicator in the instrument cluster lighting up