TPMS Anomaly

[Alb]

The car was on charge last night so I powered up and did a quick dashboard check this morning to make sure it had completed successfully.
Whilst doing this, I ran through the dash options and my attention was drawn to the TPMS Monitor.

You can see from the ambient temperature display (17 Deg C) that it was clearly not displaying current data. Although there must be a refresh cycle for this information, I'd have otherwise taken it for granted that a full power down/power up cycle would force the system to read fresh data but this doesn't seem to be the case.
Haven't taken the car out yet but I suspect that it will refresh when the car is moving so this is probably a design "feature" rather than fault. Either way, if you jump into your car first thing in the morning and check tyre pressures via the monitor, don't assume they are correct.

 

[5teep]

I think it's showing the temperature of the tyres, not the ambient temp. See mine just now.

 

[5teep]

In both images the sun is on the right side, i.e. hotter.

 

[Alb]

I think you may be missing the point?
The car hasn't been used for 24 hours and the tyres don't maintain the previous day's temperature.
It's showing the tyre temperature and pressure from the previous day and not from the present.
It's overcast (no radiated heat) so the tyre temperature should be more or less the same as ambient.

 

[Marc Nagtegaal]

thats strange. My car is parked for 6 hours but have up to date data

 

[Kithmo]

My ZS constantly shows the front left tyre to be 0.5 psi higher that the rest for some reason. They are all the same when checked with my pressure gauge.

 

[Alb]

Just took the car for a run round the block.
Once the car was moving, the readings updated one at a time until they all read correct pressure and temperature.

 

[5teep]

My ZS constantly shows the front left tyre to be 0.5 psi higher that the rest for some reason. They are all the same when checked with my pressure gauge.

Chinesium sensors

 

[Deleted member 823]

I was going to say surely they won't give accurate data until you're moving, otherwise the batteries in them will run out fairly quickly.

 

[Alb]

Think about the underlying logic.
Do you want to know your tyre is deflated before you start your journey or after you've already driven a distance down the road?
I'm not expecting it to refresh continuously, just when the car is powered up.

 

[Kithmo]

I was going to say surely they won't give accurate data until you're moving, otherwise the batteries in them will run out fairly quickly.

I've always wondered about battery life on these, assuming they have a battery and not some centrifugal force driven power supply ?

 

[Alb]

Varies from 5 to 10 years from what I've read although I've heard lots of stories about much earlier replacement because they leak. Ironic really that the thing introduced to monitor pressure actually causes the leak!

 

[LeoRBK]

I think it's showing the temperature of the tyres, not the ambient temp. See mine just now.

Yes, the tyre sensors typically sense both pressure and temperature.

 

[LeoRBK]

I was going to say surely they won't give accurate data until you're moving, otherwise the batteries in them will run out fairly quickly.

An article on internet suggests the sensor transmits data every 30 secs whilst in motion. Battery life is expected to be 5 years or 160000 miles.
When parked sensors transmit once every 20 to 30 minutes.
They are expected to immediately detect a flat tyre after park.

 

[LeoRBK]

Just took the car for a run round the block.
Once the car was moving, the readings updated one at a time until they all read correct pressure and temperature.

A drive is supposed to be needed after tyre pressure is reset. Under normal conditions it should show updated readings. It is better to clarify this with dealer. I expect them to understand TPMS by now, technology has been there for several years.

 

[C6MFC]

Hmmm some systems do not actually measure pressure they measure the internal rotating diameter of the tyre which varies with inflation (pressure/heat combined) This may not be the case on the MG but it's quite common as the relationship between pressure and temperature is complex (Gay-Lussac's law)

 

[tonymc]

Hmmm some systems do not actually measure pressure they measure the internal rotating diameter of the tyre which varies with inflation (pressure/heat combined) This may not be the case on the MG but it's quite common as the relationship between pressure and temperature is complex (Gay-Lussac's law)

I'm sure some of the early systems used the ABS sensor to detect the rolling circumfrence, the thought being that a soft/flat tyre will have a smaller diameter and will rotate faster

 

[Alb]

I have this on my Ford Focus.
They call it the Deflation Detection System and it works extremely well.
I'd prefer it over TPMS any day.

 

[LeoRBK]

I have this on my Ford Focus.
They call it the Deflation Detection System and it works extremely well.
I'd prefer it over TPMS any day.

The same article mentioned this. They called it indirect TPMS and said it is an inaccurate system and used for run-flat tyres. I will try to find the link and post it if I can.

 

[Alb]

It's actually both accurate and dependable.
Had a chance to test it very recently when I replaced an almost new tyre (7mm tread) because of a puncture. I deliberately didn't reset the DDS to see if it would recognise the very small difference in rolling radius between a new tyre and one with a couple of millimetres less tread.
Half a mile down the road and it gave me a warning so no complaints about that.
The beauty of the system is there's nothing in it likely to fail or wear out over time. Very much the opposite of TPMS.