Tyre pressure sensors?

weirdfish · Post by **weirdfish** » Fri May 04, 2012 10:59 am

Am I right in thinking that the pressure sensors are monitoring a pre- set value that is typed in to the cars computer, and thus if you haven't got the pressures within a certain parameter of these settings then the alarm will be activated.
Also, as I understand it, the spare, space saver, has also got a sensor fitted, if this isn't in the car would this trigger the alarm.

Rusty · Post by **Rusty** » Fri May 04, 2012 11:06 am

Not sure about the sensors fitted in the wheels, mine uses the abs sensors to calculate if one wheel running st a different speed to the others.

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X5Sport · Post by **X5Sport** » Fri May 04, 2012 11:10 am

Unless you have a V8 there are no sensors in the running wheels or spare. No idea if even then the spare has one? I think that they may only be active if the wheels are rotating, so if there is one in the spare it would have powered down.

The non-sensor system uses variations in rotation between each wheel, and once any of them varies away from the value determined when the pressure/system was last reset with the button, brings a warning light on.

weirdfish · Post by **weirdfish** » Fri May 04, 2012 11:14 am

I understand how the ABS type work, rolling radius etc.and you teach it every time you change anything, but as you say, on the V8 the sensors are on the valve itself.

X5Sport · Post by **X5Sport** » Fri May 04, 2012 11:33 am

System might only monitor four active channels so the spare gets ignored unless in use? Nothing obvious in a US handbook, sorry.

Raj · Post by **Raj** » Fri May 04, 2012 12:23 pm

The type with the sensor on the back of the valve is a pressure sensor. It is still set using the button when you have set the tyre pressures. It transmits to a receiver located at each corner. It monitors the individual pressure in that wheel alone to the receiver. So the spare if sat in the boot will not trigger the alarm.

Also I don't think the type of system is model specific is it. I thought I was just a change over at certain time period (for example facelifts use abs monitoring and pre-facelift use pressure sensors???). My 4.8 uses abs monitoring.

weirdfish · Post by **weirdfish** » Fri May 04, 2012 5:05 pm

Raj,
As ever mate you are spot on, the space saver does not have a sensor, but a normal size spare does.
And yes, the tyres are monitored, but it is a pre-set value, as per the handbook, anything outside of this will activate the alarm.
Isn't it wonderful when you actually read the instructions for something, but we are men, aren't we?

shadrack · Post by **shadrack** » Fri May 04, 2012 6:25 pm

[quote=""weirdfish""]Raj,
As ever mate you are spot on, the space saver does not have a sensor, but a normal size spare does.
And yes, the tyres are monitored, but it is a pre-set value, as per the handbook, anything outside of this will activate the alarm.
Isn't it wonderful when you actually read the instructions for something, but we are men, aren't we?[/quote]
what so you've found usefull information in the instructions?? na dont believe that they come free with everything to use as firelighters dont they?

Raj · Post by **Raj** » Fri May 04, 2012 8:11 pm

[quote=""weirdfish""]Raj,
As ever mate you are spot on, the space saver does not have a sensor, but a normal size spare does.
And yes, the tyres are monitored, but it is a pre-set value, as per the handbook, anything outside of this will activate the alarm.
Isn't it wonderful when you actually read the instructions for something, but we are men, aren't we?[/quote]

Out of interest, do you not have a reset button then, as I based my answer on my E46 which used the pressure sensor system but I still had a reset button to set the value.

weirdfish · Post by **weirdfish** » Fri May 04, 2012 8:54 pm

[quote=""Raj""][quote=""weirdfish""]Raj,
As ever mate you are spot on, the space saver does not have a sensor, but a normal size spare does.
And yes, the tyres are monitored, but it is a pre-set value, as per the handbook, anything outside of this will activate the alarm.
Isn't it wonderful when you actually read the instructions for something, but we are men, aren't we?[/quote]

Out of interest, do you not have a reset button then, as I based my answer on my E46 which used the pressure sensor system but I still had a reset button to set the value.[/quote]

Yes, you do have a reset button, but you still need to have the pressures within a certain parameters, as defined in the handbook, otherwise the alarm will be activated.

kkodal78 · Post by **kkodal78** » Fri May 04, 2012 9:32 pm

RDC which is next to DSC. thats to reset the tpms.

Raj · Post by **Raj** » Fri May 04, 2012 10:36 pm

[quote=""weirdfish""]

Yes, you do have a reset button, but you still need to have the pressures within a certain parameters, as defined in the handbook, otherwise the alarm will be activated.[/quote]

Hmm, I'm positive that when you set using the RDC button it sets the sensors to whatever the current pressures are as the set value then monitors within that.

Easy test will be reduce the pressure in one tyre and reset the system using RDC button and switch on car as it should ping straight away if it as you have interpreted the book. Just a thought.

weirdfish · Post by **weirdfish** » Fri May 04, 2012 11:43 pm

[quote=""Raj""][quote=""weirdfish""]

Yes, you do have a reset button, but you still need to have the pressures within a certain parameters, as defined in the handbook, otherwise the alarm will be activated.[/quote]

Hmm, I'm positive that when you set using the RDC button it sets the sensors to whatever the current pressures are as the set value then monitors within that.

Easy test will be reduce the pressure in one tyre and reset the system using RDC button and switch on car as it should ping straight away if it as you have interpreted the book. Just a thought.[/quote]

You could be right, it just implies in the handbook that you set the pressures as per the chart on a certain page, then you go through the teaching process.
It might of course just be saying that they are the reccomended pressures. As you say, the only way to test the theory is to try and fool it by reducing, or even over pressurising the tyres.
Job for the morning.

Raj · Post by **Raj** » Sat May 05, 2012 12:02 am

[quote=""weirdfish""]

You could be right, it just implies in the handbook that you set the pressures as per the chart on a certain page, then you go through the teaching process.
It might of course just be saying that they are the reccomended pressures. As you say, the only way to test the theory is to try and fool it by reducing, or even over pressurising the tyres.
Job for the morning.[/quote]

Let us know the results.

Rusty · Post by **Rusty** » Sat May 05, 2012 9:22 am

It would make sense that the system would take the value from each sensor (each sensor will read differently as I'm sure they re not THAT accurate) when it is reset, and then monitors this value and if it moves out of a preset tolerance, the 'bing' occurs.

Simple software really

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