tyre pressure warning light

[NemesisUK]

3 minutes ago, Hadrian said:

My TPMS warning light came on again today on start-up.  Due to another sudden change in the weather. It did it the last time the temperature dropped.

All tyre pressures OK, and reset....  again.

You say the pressures were OK? So why did the TPMS light come on?

The light coming coming on would indicate the pressure it is monitoring has dropped below the level set during initialisation.

Does your model display the actual tyre pressures? 

[Hadrian]

When I say the tyre pressures were ok, I mean they were within acceptable limits. The pressures in all tyres had dropped  around 5 psi  due to the drop in temperature overnight.

The  sensors in the Lexus do seem to be a lot more sensitive than those in my BMaxx. They didn't register a puncture until it had dropped by about 10 psi.

No, mine doesn't display actual pressure. I wasn't aware any did.

[NemesisUK]

My RC can display the pressure for each tyre individually.

Did the BMax have valve pressure sensors, or was it the indirect system?

[rayaans]

2 hours ago, Hadrian said:

My TPMS warning light came on again today on start-up.  Due to another sudden change in the weather. It did it the last time the temperature dropped.

All tyre pressures OK, and reset....  again.

Why do you keep resetting the tyre pressures.

Just leave it as it is and forget about it. If the pressure is right the light will go away by itself after topping up. 

[OldTrout]

1 hour ago, Hadrian said:

When I say the tyre pressures were ok, I mean they were within acceptable limits. The pressures in all tyres had dropped  around 5 psi  due to the drop in temperature overnight.

 

If you start from 35psi then 5psi drop is about 14%. To achieve this by temperature alone would require about 40 degrees drop. Unlikely in England I think?

John

 

[Guest]

Mine seems to activate at a drop if 0.2 - 0.3 bar when cold. Fine by me as like to keep them accurate. Problem is we have had some 10+ degree ambient temp swings. So I've been ignoring morning warnings for now until its constantly a lower temp. So about now :(

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[Hadrian]

Talking to the chap at my local Lexus service centre, (where I went to find out how to do a reset) it's a very common occurrence as the sensors are so sensitive.

[NemesisUK]

But as @rayaans says, one doesn't have to 'reset' the system. Simply correct the tyre pressures and the light goes out.

Only time one needs to reset is if, for example, one fully loads the vehicle and increases the tyre pressures in accordance with the handbook recommendations.

Resetting using the button just tells the system the current pressure readings are the benchmark  values.

[Hadrian]

Easier to do a reset.

[rayaans]

4 hours ago, Hadrian said:

Easier to do a reset.

No its not because you don't know what the pressures are. Just fill up and itll go away if the pressure is right.

If the light is still on it means your pressures are wrong.

[wharfhouse]

I read that all tyres filled with air lose some pressure over time. The reason was that oxygen molecules are small enough to be able to escape through tyre rubber (obviously very slowly) but the larger nitrogen molecules can not. As air is 20% oxygen the tyres will over time lose up to 20% naturally (for the same temperature). That was the rationale behond inflating tyres with pure nitrogen - more stable pressures and no pressure reduction over time. 

Sounds reasonable to me but don't shoot the messenger if it turns out to be BS though...!