Tyre Pressure Monitor

[ScotMac]

Does anyone know if the TPM "valves" on each wheel "last for ever".

I inflated all my tyres but the system still reads the old pressure. After a while the rear tyre pressures went up but the fronts remained at the old pressure.

Maybe try selecting a different wheel/combination on the MFD menu. Go for a drive, then stop and set the correct wheel/tyres and repeat the drive. At a guess that should reset the TPMS system.

Thanks, I will try that. I increased the pressures quite a bit so was surprised to see basically the same pressure being indicated.

[Nuclear Nick]

Porsche and the majority of the VAG cars use Indirect TPMS, which uses the anti-lock wheel speed sensors to measure the rate of revolutions relative to each wheel. A change of pressure causes a change of wheel diameter and revolution speed, which is picked up by the car's computer. It is not as accurate as direct TPMS, which use pressure transmitters in each wheel and provides tyre pressure readings when the car is stationary, but this is more costly and the batteries only last about ten years

This from the manual tells me that the wheel 'transmitters' are feeding actual pressures to the instrument panel. Also, if there was a fault it would throw up an alarm:

Attention to TPMS Malfunction Indicator
Your vehicle has also been equipped with a TPMS malfunction indicator to indicate when the system is not operating properly.

The TPMS malfunction indicator is combined with the low tire pressure telltale.

When the system detects a malfunction, the telltale will flash for approximately one minute and then remain continuously illuminated. This sequence will continue upon subsequent vehicle start-ups as long as the malfunction exists.

When the malfunction indicator is illuminated, the system may not be able to detect or signal low tire pressure as intended.

TPMS malfunctions may occur for a variety of reasons, including the installation of replacement or alternate tires or wheels on the vehicle that prevent the TPMS from functioning properly.

Always check the TPMS malfunction telltale after replacing one or more tires or wheels on your vehicle to ensure that the replacement or alternate tires and wheels allow the TPMS to continue to function properly.
The warning light in the instrument panel lights up:

When a loss in pressure is detected (warning light: lights up continuously).
In the event of a defect in the Tire Pressure Monitoring System or a temporary fault (warning light: flashes for 60 seconds, then lights up continuously).
When learning newly fitted wheels/wheel transmitters, as long as the vehicle’s own wheels have not yet been detected (warning light: flashes for 60 seconds, then lights up continuously).
A warning message also appears on the multi-function display of the instrument panel.

Please see the chapter “OVERVIEW OF WARNING AND INFORMATION MESSAGES” on page 142.
The tire pressure warning light on the instrument panel goes out only when the cause of the fault has been rectified.

Overview of Tire Pressure Monitoring System functions
The Tire Pressure Monitoring System offers the following functions:

Display of the actual tire pressure while the vehicle is in motion.
Tire pressure warnings in two stages (yellow and red warning).
In the “TPMS” menu, the settings “Fill info” (display of the deviation from the required pressure, refill pressure), “Tire type” and “Full load” are available when the vehicle is stationary.

Tire pressure display on the multi-function display

Selecting the TPMS function on the multi-function display



The “TPMS” function displays the temperaturedependent tire pressures (actual pressures) in the four wheels when the vehicle is traveling at a speed of more than approx. 16 mph (25 km/h).

You can watch the tire pressure rise as the temperature increases when driving.

Information
The display of the actual pressures is only for information purposes.

Under no circumstances should the tire pressures be changed based on this display.

[Mistertoad]

I think this confirms it is an indirect TPMS:

"The “TPMS” function displays the temperaturedependent tire pressures (actual pressures) in the four wheels when the vehicle is traveling at a speed of more than approx. 16 mph (25 km/h).

You can watch the tire pressure rise as the temperature increases when driving."

The GT V8 Bentley Owners Manual makes no mention of having to travel above a certain speed to get readings, In fact it says it compensates for ambient air and tyre temperature to allow the driver to adjust the tyre pressures with the tyres hot or cold, which means it must be a direct TPMS.
I have just added some air to a tyre and the rise in pressure was indicated

My eldest son has been a development engineer with Audi R@D in Ingolstadt for a very long time and a couple of years ago he told me TPMS was now a very low cost system as it used cheap sensors to talk to the Anti-skid system. Those must be the gizmos that were missing from Bigboyrolo's newly painted wheels.

[Nuclear Nick]

Yes, I can see it can be read that way, but I don't see how it could 'Display the actual tire pressure while the vehicle is in motion' unless the sensors are transmitting pressure data. I had a BMW some years ago and that certainly had the indirect system that measured wheel rotation rather than tyre pressure. Indeed it had no sensors in the wheel rims unlike the Macan which clearly does. Why have sensors if they are not transmitting pressures to the car, and how otherwise could pressures be displayed in the instrument panel? My motorcycle also has wheel sensors and it displays actual pressures. Like the Macan, it doesn't display pressures until the bike has been moving for a minute or two.

[goron59]

The Wikipedia page for modern iTPMS gives a reasonable explanation, even if you don't understand the science.

[Mistertoad]

My Cayenne picked up a screw which caused a slow puncture in the FOS tyre. The next day the TPMS warned me about a drop in pressure in that tyre after the car had travelled a couple of hundred yards. I have read that to prolong battery life some TPMS systems need the wheels to be rotating before the sensors work. This could account for no warnings when stationary, but I can't see why the Macan TPMS is so different the Bentley as they are both part of VAG.

[Bigboyrolo]

I think this confirms it is an indirect TPMS:

"The “TPMS” function displays the temperaturedependent tire pressures (actual pressures) in the four wheels when the vehicle is traveling at a speed of more than approx. 16 mph (25 km/h).

You can watch the tire pressure rise as the temperature increases when driving."

I have just added some air to a tyre and the rise in pressure was indicated

My eldest son has been a development engineer with Audi R@D in Ingolstadt for a very long time and a couple of years ago he told me TPMS was now a very low cost system as it used cheap sensors to talk to the Anti-skid system. Those must be the gizmos that were missing from Bigboyrolo's newly painted wheels.

Yes indeed Mrtoad. The senders are generic VW group, when I had them in my hands prior to refitting they all had VW part numbers, so nothing special for Porsche. I raised the pressures before driving to Euroland and set them for ' Full Load' (Mrs B takes a lot of stuff). After a few miles the dash indicator panel went crazy with warnings for each tyre, not of pressure, but numeric of -16 to +5. So I deleted 'Full Load' and all was fine. In Italy I had them all raised to 36/39 (2.5/2.7 bar I think) indicated pressures when driving rose to 41/46! So I've lowered them all using my tyre guage to 35/38 and all seems fine with 'Full Load' selected.
How did we manage before TPMS? I would be fine without it. An EU requirement since a few years ago.

[Bigboyrolo]

Does anyone know if the TPM "valves" on each wheel "last for ever".

They do not. The built in batterys have a 4-6 yr life. From examing them when they were off my wheels, they seemed to be sealed units. Replacements are around £75 each. They are VW parts.
My tyre dealer had an electronic detector that gave pressure and temperature transmitted by each one. Perhaps it also indicates battery life.

[ScotMac]

Does anyone know if the TPM "valves" on each wheel "last for ever".

They do not. The built in batterys have a 4-6 yr life. From examing them when they were off my wheels, they seemed to be sealed units. Replacements are around £75 each. They are VW parts.
My tyre dealer had an electronic detector that gave pressure and temperature transmitted by each one. Perhaps it also indicates battery life.

Thanks. I think they will also suffer badly from corrosion.

"Modern" cars are becoming more and more expensive to run as they get older

[Nosmo]

This doesn't make sense at all:

The “TPMS” function displays the temperaturedependent tire pressures (actual pressures) in the four wheels when the vehicle is traveling at a speed of more than approx. 16 mph (25 km/h).

You can watch the tire pressure rise as the temperature increases when driving.

Information
The display of the actual pressures is only for information purposes.

Under no circumstances should the tire pressures be changed based on this display.

Having a gadget that is not to be trusted but indicates actual pressures? Really?