Tyre valves

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SeaCrosser
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Post by SeaCrosser »

I noticed slight marking on the front tyres, indicating under-inflation and on checking them, found they were indeed a few pounds under.
That was about a month ago. I had a service done this week and the garage told me they had pumped them up to the correct pressure ( as on the plate by the driver's door).
I told them I'd checked a few weeks ago and they said they had heard that tyre valves can fail after a couple of years.
Has anyone else heard the same?
The TPMS warning light hadn't come on by the way.
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Juan Sheet
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Post by Juan Sheet »

Just for you to be aware, the TPMS doesn’t use the old type of valve sensors. It uses an indirect TPMS system handled by the ESP. Therefore, valves should be replaced when the tyres are replaced which is normal practice.

You may have a faulty valve, a slow puncture or bad tyre seal, or even a badly calibrated / faulty tyre inflation device that can cause this.
SeaCrosser
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Post by SeaCrosser »

That's interesting @Juan Sheet.

i'm heading down to the Costa Brava area next week and with 20000 miles on the tyres, wondered about swapping them round.

(Back in the day, this used to be a Thing- for the younger readers).

The reply I got was along the lines of, the TPMS sensors are coded to specific wheels- ie NSF, OSR etc. So swapping them would give a reading for a tyre in the wrong place.
Would an indirect system still behave like this?

Either way, I'm not going to faff about with a tyre swap, but I will definitely need to check the pressures very regularly in Spain.
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Juan Sheet
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Post by Juan Sheet »

No that's not relevant to indirect TPMS as there is no direct electronic contact between the wheels and the ESP system.

As for wheel position, as far as the vehicle and the ESP ECU is concerned, it is the wheel speed sensor (ABS Sensor if you like) that is responsible for the relevant wheel. These are of course fixed and another reason why this system does not provide tyre pressure values on the display.

The indirect system on your vehicle works by by analysing any change in the diameter of the wheels or in the physical behaviour of the tyres. The dynamic stability control ECU estimates the pressure of the tyres from the information transmitted by the wheel speed sensors. The ESP ECU compares the wheel speeds and the physical behaviour of the tyres in relation to the ambient temperature and as a function of these values determines the condition of the tyres, and sends this data to the BSI (Main computer).

If the pressure estimated by the dynamic stability control ECU is below the tolerated thresholds, the built-in systems interface informs the driver of the condition of the tyres via the instrument panel or the multifunction screen. It's another reason why you need to initialise the TPMS via the touchscreen each time you check your tyre pressures (when cold).
JFS Dorset
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Post by JFS Dorset »

I once had a problem with a slow puncture or so I thought. Local garage couldn’t find one so pumped up to correct pressure my warning came back a few hours afterwards. The problem was a defective dust cap. I took them off to check tyres before a long journey. The tiny washer in one of them must have fallen out. I only found this out after reinflation and leaving dust camp off! New dust caps fitted no fury problem. I couldn’t find this solution on google. Lots of other ‘potential causes’ but not dust caps! One for the memory bank!
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the2ems
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Post by the2ems »

JFS Dorset wrote: Fri Jul 01, 2022 5:38 am I once had a problem with a slow puncture or so I thought. Local garage couldn’t find one so pumped up to correct pressure my warning came back a few hours afterwards. The problem was a defective dust cap. I took them off to check tyres before a long journey. The tiny washer in one of them must have fallen out. I only found this out after reinflation and leaving dust camp off! New dust caps fitted no fury problem. I couldn’t find this solution on google. Lots of other ‘potential causes’ but not dust caps! One for the memory bank!
Dust caps are there just to keep the valve clean, not to keep air in. You must have had a leaky valve.
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JFS Dorset
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Post by JFS Dorset »

No the dust cap was pushing in the valve and release air. The valve was fine! Didn’t explain very well!
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the2ems
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Post by the2ems »

JFS Dorset wrote: Sat Jul 02, 2022 4:00 pm No the dust cap was pushing in the valve and release air. The valve was fine! Didn’t explain very well!


Ah right. That makes more sense. 8-)
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SeaCrosser
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Post by SeaCrosser »

Dodgy dustcaps?

That's definitely worth checking. I'm might pick up a spare set before I go off on my travels.

:idea:
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routemaster1
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Post by routemaster1 »

I have a new car (non-Citroen) with indirect TPMS. On holiday in Austria a couple of weeks ago we had a low pressure warning. In our case the system informed of a puncture on the rear left tyre. Citroen could easily do this, but there is no indication of location. For info, the tyre pressure should have been 2.8 bar, but was actually 2.3 bar.
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