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[LC0112G]

I suspect the same will be true for any bluetooth (or similar tech) based system. Which basically means any system that can give you the individual tyre pressures (in psi/kpa) on the dash screen.

Thats not strictly true.  Certainly our cars learn the position - and its defo not bluetooth as its on the 433MHz licence exempt band.  My car is a bit old so doesn't, as far as I can work out, give the actual readings, only alert you when one tyres is down a bit, and tells you which one.

Her motor uses exactly the same sensors as mine, and does give the pressure readouts on the dash, but is a little newer than mine.

Yeahbut, how does the car actually know which wheel is in which location? AFAIK there is no electrical connection between the chassis and hub, so all comms have to be done over RF, and RF has a range of many meters. Can't see signal strength being a particularly reliable indication. I suppose the sensor might know if it's rotating clockwise or anticlockwise which would narrow the choice down to two of four, but can't see how it could reliably tell if it's front or rear, assuming identical age, make and size of tyres.

If you've had to tell it somewhere during setup that sensor #123456 is OSF and sensor #567890 is OSR then odds are it isn't going to care if you swap the OSR and OSF around whilst there is no flat, coz it's still talking to both sensors.  But if sensor #123456 detects a flat in it's tyre, then where it's actually positioned on the car does matter, and if it's been told #123456 is OSF can it really learn on it's own that it's really the OSR and report it correctly? If so, how?

[Kevin Wood]

Yeahbut, how does the car actually know which wheel is in which location?

The sensors count wheel rotation and so does the ABS ECU, so it's easy to correlate the two and figure out which sensor is on which wheel.

[Doctor Gollum]

………..
my advice would always be to check all 4 tyres in the event of a TPMS warning just in case.

On my bmw the display showed what the tyre pressure is on all 4 corners. On my Audi, the display shows ‘Under inflated tyre’, which translates to ‘ You have an under inflated tyre, find out which one yourself’. 
I have no option but to check all 4 tyre pressures. 

In part because they're tighter than a ducks arse, VAG stuff tends to rely on the ABS system to detect rolling radius discrepancies and translates these to an under inflated tyre.

An unintended consequence is that you have to check all four tyres to establish the low one and correct it. This isn't necessarily a bad thing as you're supposed to check them once a week anyway... Obviously most people don't bother, in part because of TPMS systems  Ironic isn't it...

[Auto Addict]

Astra K gives a reading on all 4 tyres,

It has a reset button to enable it to recalculate the sensors.

What they don't tell you it works with a separate menu that has to be set according to the load in the car.

[Auto Addict]

The good news is my car insurance has gone down by £50 this year.

Still astronomical because of my age.

[Doctor Gollum]

The good news is my car insurance has gone down by £50 this year.

Still astronomical because of my age.

You should get a discount because it's fire engine red...

[LC0112G]

Yeahbut, how does the car actually know which wheel is in which location?

The sensors count wheel rotation and so does the ABS ECU, so it's easy to correlate the two and figure out which sensor is on which wheel.

Yeahbut no. Only works if the initial programming of sensor to wheel location is correct, and maintained. Put two identical rims, two identical tyres on those rims then the revs per mile are identical. The ABS ECU cannot then tell the difference between the two, and you can swap tyres around willy-nilly and the car is none the wiser. It's only if/when the tyres differentially wear enough so that the diameters are different that sensors and ABS ECU's stand a chance of working out which is which.

For instance. Go to Kwik-Fit and replace all 4 tyres with new ones. Put the 4 new tyres/rims in random positions on the car. How does the car know which rim is in which position - they're all the same.

[LC0112G]

Astra K gives a reading on all 4 tyres,

It has a reset button to enable it to recalculate the sensors.

What they don't tell you it works with a separate menu that has to be set according to the load in the car.

I wonder. Next time you get a pair of tyres replaced - ideally on one axle - inflate both tyres to (say) 35 psi (or whatever your normal running pressures are. Drive a few miles and make sure the dash readout is displaying both tyre pressures correctly.

Then swap OSF and NSF around. Go for a drive. Assuming both were reading 35psi/whatever before then they should both still be reading 35psi now.

Then let some air out of the OSF, down to say 28 psi. Go for a short drive. Does the dash display correctly show the OSF as 28psi, and the NSF as 35psi, or the other way around?

[TheBoy]

I suspect the same will be true for any bluetooth (or similar tech) based system. Which basically means any system that can give you the individual tyre pressures (in psi/kpa) on the dash screen.

Thats not strictly true.  Certainly our cars learn the position - and its defo not bluetooth as its on the 433MHz licence exempt band.  My car is a bit old so doesn't, as far as I can work out, give the actual readings, only alert you when one tyres is down a bit, and tells you which one.

Her motor uses exactly the same sensors as mine, and does give the pressure readouts on the dash, but is a little newer than mine.

Yeahbut, how does the car actually know which wheel is in which location?

who knows, but it does

I know there is a antenna in each wheel arch, I assume that can either detect signal strength, or put out an ultra low power signal that has a short range for the transponder to respond.

I could read the docs, but suffer badly with CBA.  And having a Y chromosome, I couldn't possible read instructions

[TheBoy]

OK, Y degeneration is very high in me....

This is what it says, which doesn't explain how:


The TPMS can identify the position of the wheels on the vehicle and assign a
received tire pressure sensor identification to a specific position on the
vehicle, for example front left, front right, rear left and rear right. This feature is
required because of the different pressure targets and threshold that could
exist between the front and rear tires.

The wheel location is performed automatically by the CJB using an 'auto-
location' function. This function is fully automatic and requires no input from
the driver. The CJB automatically re-learns the position of the wheels on the
vehicle if the tire pressure sensors are replaced or the wheel positions on the
vehicle are changed.

The TPMS software can automatically detect, under all operating conditions,
the following:

• one or more new tire pressure sensors have been fitted
  one or more tire pressure sensors have stopped transmitting
  CJB can reject identifications from tire pressure sensors which do not belong to the vehicle
  two 'running' wheels on the vehicle have changed positions.
  If a new tire pressure sensor is fitted on any 'running' wheel, the CJB can learn
  the new sensor identification automatically through the tire learn and location process.

The tire-learn and location process is ready to commence when the vehicle
has been stationary or traveling at less than 12 mph (20 km/h) for 15 minutes.
This is known as 'parking mode'. The learn/locate process requires the vehicle
to be driven at speeds of more than 12 mph (20 km/h) for 15 minutes. If the
vehicle speed reduces to below 12 mph (20 km/h), the learn process timer is
suspended until the vehicle speed increases to more than 12 mph (20 km/h),
after which time the timer is resumed. If the vehicle speed remains below 12
mph (20 km/h) for more than 15 minutes, the timer is set to zero and process
starts again.[/i]

[TheBoy]

The tire low pressure sensor transmits by RF (315 MHz or 433 MHz depending
on market) signal. These signals contain data which corresponds to tire low
pressure sensor identification, tire pressure, tire temperature, acceleration and
tire low pressure sensor mode.
Each time the vehicle is driven, the tire pressure monitoring system module
activates each LF antenna in turn. The corresponding tire low pressure sensor
detects the LF signal and responds by modifying the mode status within the
RF transmission.
The system enters 'parking mode' after the vehicle speed has been less than
20 km/h (12.5 miles/h) for 12 minutes. In parking mode the tire low pressure
sensors transmit a coded signal to the tire pressure monitoring system module
once every 13 hours. If the tire pressure decreases by more than 0.06 bar (1
lbf/in²) the tire low pressure sensor will transmit more often as pressure is lost.
As each wheel responds to the LF signal from the tire pressure monitoring
system module, it is assigned a position on the vehicle and is monitored for
the remainder of that drive cycle in that position.
When the vehicle has been parked for more than 15 minutes and then driven
at a speed of more than 20 km/h (12.5 miles/h), the antennas fire in turn for 6
seconds on all except North American specification vehicles or for 18 seconds
on North American specification only vehicles in the following order:
Front left
Six second pause (for the tire pressure monitoring system module to detect
a response from the tire low pressure sensor)
Front right
Six second pause
Rear right
Six second pause
Rear left
Six second pause.
Each tire low pressure sensor responds in turn so the tire pressure monitoring
system module can establish the tire low pressure sensor positions at the start
of the drive cycle. This process is repeated up to three times but less if the tire
low pressure sensor positions are already known in the tire pressure
monitoring system module.
This process is known as 'Auto Location' and takes:
three to five minutes on all except North American specification vehicles to
complete, and
seven to eight minutes on North American specification vehicles to
complete.
During this period the tire low pressure sensors transmit at regular intervals:
once every 5 seconds on all except North American specification vehicles,
and
once every 15 seconds on North American specification vehicles.
For the remainder of the drive cycle the tire low pressure sensors transmit
once every 60 seconds or if a change in tire pressure is sensed until the
vehicle stops and the tire pressure monitoring system returns to parking
mode.
Once the wheel position is established, the antennas stop firing and do not
fire again until the vehicle has been parked for more than 15 minutes. The
signal transmissions from each tire low pressure sensor continue at one
minute intervals whilst the vehicle is being driven. This transmission is to
monitor the tire pressure. The warning occurs at 25% deflation and comprises
the low tire pressure warning indicator and an appropriate message displayed
in the instrument cluster message center. The message center will also display
additional information about the position of the affected wheel(s).

[Migv6 le Frog Fan]

What a load of Palaver.
My tyre pressure monitor looks like this and has served me perfectly well for almost 50 years , well not the same one but the same type.

https://www.ebay.co.uk/itm/153516528773?_skw=tyre+pressure+gauge&itmmeta=01K26SVST9332N3330A4WVBGAG&hash=item23be4c5485:g:aFIAAOSwSOditGsa&itmprp=enc%3AAQAKAAAA0FkggFvd1GGDu0w3yXCmi1fp%2F1Zla9121Jkk%2B1QEaB4eHrO5k9gnAbgFi7%2B3qyCNU2qxxq%2BC%2BLToW8mLStBHLkxvRABAmBP%2Bqf3CSU856YvEmmLSpchMQtNwwOT79HzmZ5pBbcmr0IaZwIHtu1Ph51yfiJ16PL6e68N4nm7IDLt9t%2Br3RRnxTbxHHwOPPJXGhF6spRsBSwi9ZmfpMkZ71ONeYQN5Bani%2FsBHMB1mETSW1XmNcpmw0Zjb1Pvg8B4n6c8Evd7hFCj%2BRiDn6cdEU1c%3D%7Ctkp%3ABk9SR7Kd79mRZg

This modern nonsense is over complication for the sake of it.
If you cba to check tyre pressures once a week you shouldnt be allowed to drive. 

[Rangie]

What a load of Palaver.
My tyre pressure monitor looks like this and has served me perfectly well for almost 50 years , well not the same one but the same type.

https://www.ebay.co.uk/itm/153516528773?_skw=tyre+pressure+gauge&itmmeta=01K26SVST9332N3330A4WVBGAG&hash=item23be4c5485:g:aFIAAOSwSOditGsa&itmprp=enc%3AAQAKAAAA0FkggFvd1GGDu0w3yXCmi1fp%2F1Zla9121Jkk%2B1QEaB4eHrO5k9gnAbgFi7%2B3qyCNU2qxxq%2BC%2BLToW8mLStBHLkxvRABAmBP%2Bqf3CSU856YvEmmLSpchMQtNwwOT79HzmZ5pBbcmr0IaZwIHtu1Ph51yfiJ16PL6e68N4nm7IDLt9t%2Br3RRnxTbxHHwOPPJXGhF6spRsBSwi9ZmfpMkZ71ONeYQN5Bani%2FsBHMB1mETSW1XmNcpmw0Zjb1Pvg8B4n6c8Evd7hFCj%2BRiDn6cdEU1c%3D%7Ctkp%3ABk9SR7Kd79mRZg

This modern nonsense is over complication for the sake of it.
If you cba to check tyre pressures once a week you shouldnt be allowed to drive. 

.

Agree entirely , I've had my Dunlop pressure gauge for as long as I can remember always check mine every week along with oil water & screenwash.

[Auto Addict]

What a load of Palaver.
My tyre pressure monitor looks like this and has served me perfectly well for almost 50 years , well not the same one but the same type.

https://www.ebay.co.uk/itm/153516528773?_skw=tyre+pressure+gauge&itmmeta=01K26SVST9332N3330A4WVBGAG&hash=item23be4c5485:g:aFIAAOSwSOditGsa&itmprp=enc%3AAQAKAAAA0FkggFvd1GGDu0w3yXCmi1fp%2F1Zla9121Jkk%2B1QEaB4eHrO5k9gnAbgFi7%2B3qyCNU2qxxq%2BC%2BLToW8mLStBHLkxvRABAmBP%2Bqf3CSU856YvEmmLSpchMQtNwwOT79HzmZ5pBbcmr0IaZwIHtu1Ph51yfiJ16PL6e68N4nm7IDLt9t%2Br3RRnxTbxHHwOPPJXGhF6spRsBSwi9ZmfpMkZ71ONeYQN5Bani%2FsBHMB1mETSW1XmNcpmw0Zjb1Pvg8B4n6c8Evd7hFCj%2BRiDn6cdEU1c%3D%7Ctkp%3ABk9SR7Kd79mRZg

This modern nonsense is over complication for the sake of it.
If you cba to check tyre pressures once a week you shouldnt be allowed to drive. 

.

Agree entirely , I've had my Dunlop pressure gauge for as long as I can remember always check mine every week along with oil water & screenwash.

I go round and kick each tyre on a daily basis.

[TheBoy]

What a load of Palaver.
My tyre pressure monitor looks like this and has served me perfectly well for almost 50 years , well not the same one but the same type.

https://www.ebay.co.uk/itm/153516528773?_skw=tyre+pressure+gauge&itmmeta=01K26SVST9332N3330A4WVBGAG&hash=item23be4c5485:g:aFIAAOSwSOditGsa&itmprp=enc%3AAQAKAAAA0FkggFvd1GGDu0w3yXCmi1fp%2F1Zla9121Jkk%2B1QEaB4eHrO5k9gnAbgFi7%2B3qyCNU2qxxq%2BC%2BLToW8mLStBHLkxvRABAmBP%2Bqf3CSU856YvEmmLSpchMQtNwwOT79HzmZ5pBbcmr0IaZwIHtu1Ph51yfiJ16PL6e68N4nm7IDLt9t%2Br3RRnxTbxHHwOPPJXGhF6spRsBSwi9ZmfpMkZ71ONeYQN5Bani%2FsBHMB1mETSW1XmNcpmw0Zjb1Pvg8B4n6c8Evd7hFCj%2BRiDn6cdEU1c%3D%7Ctkp%3ABk9SR7Kd79mRZg

This modern nonsense is over complication for the sake of it.
If you cba to check tyre pressures once a week you shouldnt be allowed to drive. 

I kinda agree, and do weekly fortnightly checks manually, albeit with a posher gauge.

TPMS does have a usefulness though to inform a driver of a puncture picked up during a journey, or even of low pressure between manual checks.  And knowing earlier if picking up a nail on a fast road can be the difference between being able to stop and save the tyre, or a big blowout and a wrecked tyre.


A bit like the coolant level warning is handy rather than waiting for temp gauge or boiling should a big coolant leak develop mid journey