C5-Tyre(s) Deflated warning

oldfruit · Post by **oldfruit** » 21 Oct 2009, 11:02

I have this message displayed after a couple of hundred yards every trip, but can find no under-pressure tyre. Could it be that a sensor was damaged when I had new tyres fitted and would a Lexia tell me which one was telling porkies?

Peter

Post by **Paul-R** » 21 Oct 2009, 13:55

It certainly sounds like a faulty/damaged sensor. I am not sure whether a Lexia cold tell you which one is damaged but you can find out another, if time consuming, way.

If you replace one wheel after another with your spare and then take the car out for a brief drive any working vlave will then increase the number of tyres warned about. The one wheel that DOESN'T increase the count is the faulty one.

If you can claim against the tyre place don't forget to claim for the fact that a replacement valve has to be paired up with the ECU. This is a Lexia job. Unfortunately you also need a small device called a Protoctair to energise the new valve. I don't know of anyone, barring Citroen dealers, who have this.

Philjw · Post by **Philjw** » 21 Oct 2009, 16:16

On my 05 MK2 C5 there is a dash indicating which tyre is thought to be under pressure. It comes up next to an image of the car on the screen.
Do you not have this?

Phil

wheeler · Post by **wheeler** » 21 Oct 2009, 21:26

Mk1 & mk2 use a different system. On the mk1 it just knows there are 4 sensors & can tell you how many tyres are low in pressure but it doesent know which ones. The mk2 is a bit more advanced, it knows where each sensor is & learns their positions once you start driving. This means if you swap the wheels front to rear for example it just re-learns where each sensor is.
You could find the faulty sensor with a lexia but you would need the Protoctair aswell

Philjw · Post by **Philjw** » 22 Oct 2009, 12:30

Re Wheeler's post I have in the past bought 4 tyres on a deal at Costco and only fiited two at a time. Costco insist on fitting the new ones at the rear and because they think the sensors are matched to their original position on the car they end up changing all 4 covers to keep the rim in the original place. From what you say here that is not needed since the car learns where each sensor is to be found. That could save a lot of tyre changes. Is this documented anywhere?

Phil

JohnD · Post by **JohnD** » 22 Oct 2009, 16:24

A couple of times I've switched front to rear and it doesn't upset the sensors. That's on a Mk2 model.

wheeler · Post by **wheeler** » 22 Oct 2009, 16:31

Costco recomend fitting new tyres to the rear on all cars even without pressure monitoring systems because michelin recomend this.
There are emitters behind the front wheelarch liners on the mk2 that are used to identify the positions of the sensors. You can also have 8 sensors programed to the mk2 incase you have a set of winter tyre etc.

cachaciero · Post by **cachaciero** » 22 Oct 2009, 22:32

Paul-R wrote: If you can claim against the tyre place don't forget to claim for the fact that a replacement valve has to be paired up with the ECU. This is a Lexia job. Unfortunately you also need a small device called a Protoctair to energise the new valve. I don't know of anyone, barring Citroen dealers, who have this.

My understanding of the Protocair tool is that it used for calibration of the sensor rather than energising but I could be wrong

Cachaciero

Post by **Paul-R** » 22 Oct 2009, 23:34

It may do that as well but I don't know. I was under the impression that the valves are preset and are not adjustable.

This pdf is for the Protoctair mini as used by my local Citroen dealer in association with a Lexia http://www.one-too.com/German/Fiches/Pr ... r_mini.pdf . As you can see it talks of a 125KHz exciter. From reading elsewhere I understand this causes the valve to send out its radio signal. The Protoctair is moved from wheel to another as instructed by the Lexia and this causes the valve to be recognised by the ECU.

I've been unable to find an exciter at a rasonable price - about £140 seems to e the cheapest. Being a tinkerer I've considered building my own exciter but haven't got around to it yet. Maybe one day.

wheeler · Post by **wheeler** » 23 Oct 2009, 09:40

Paul-R wrote: As you can see it talks of a 125KHz exciter. From reading elsewhere I understand this causes the valve to send out its radio signal. The Protoctair is moved from wheel to another as instructed by the Lexia and this causes the valve to be recognised by the ECU.

Thats exactly what it does & by doing this it can find sensors that are not responding.
The emitters behind the front wheel arches on the mk2 do the same kind of thing which is how it can identify their positions although new sensors still need to be programed with Lexia & the valve exciter.

cachaciero · Post by **cachaciero** » 23 Oct 2009, 20:43

O.K I am a little confused as to how these things work, I've done some reading in the last 24 hrs but it would appear that there are many different kinds of these things some of which work more intelligently than others. Anyway back to the ones fitted on early C5's.
My understanding is that under normal operation these devices transmit data which gets picked up by a reciever. One thing that seems to be common is that the transmitted data stream consists of an ID plus other data. The on board electronics need to know the ID of the devices fitted at each corner.

Question 1 do these devices continuously transmit data or only when tyre pressure falls below a certain level? If as I suspect it only happens below a certain tyre pressure does anyone know what the pressure threshold is ?

This would explain the need for an exciter which will force the device to send it's data stream so that the Lexia can identify what is where without the requirement to let air out of the tyre which would / should cause it to transmit naturally.

Letting the air out of the tyres and then pumping them up again (one by one!) may seem a bit of a long winded way of registering these things but I can't see why it wouldn't work....... maybe :_/

Cachaciero

Post by **Paul-R** » 24 Oct 2009, 21:45

I can't find where I originally found this information so I can't put exact figures down but, as far as my Phase I C5 is concerned it goes something like this.

When stationary and with the tyres at correct pressure (or at least above the warning pressure level) the valves emit a radio signal every so many minutes (about an hour I think). When the vehicle is on the move this periodicity increases (to every 10 minutes I think). If a tyre pressure falls below the warning level then the signal changes and the periodicity increases to frequent (every 30s or minute IIRC).

Sorry to be so vague. I HATE not being able to be accurate!

Post by **Paul-R** » 24 Oct 2009, 21:49

Having read ALL of your post I don't think that your method of lowering tyre pressures will work as the Lexia expects the response from whichever valve it asks about pretty quickly.

I doubt whether anyone could deflate and then reflate four tyres so quickly.

cachaciero · Post by **cachaciero** » 24 Oct 2009, 23:28

Paul-R wrote:Having read ALL of your post I don't think that your method of lowering tyre pressures will work as the Lexia expects the response from whichever valve it asks about pretty quickly.

I doubt whether anyone could deflate and then reflate four tyres so quickly.

Ah!... well it was only thought, if it works the way you say it does then I have a feeling that a low pressure signal would not be enough to cause registration, after all if it transmits on a regular basis when the tyre is good and it won't register why would it do it flat:-).
I wonder if the initiator just generates 125K hz with no embedded data if so it should be simple enough to make one.

Cachaciero

Post by **myglaren** » 24 Oct 2009, 23:49

I don't have them on my C5 but I have read that on changing wheels around, especially fitting the spare, error messages can be thrown up. They seem to be somewhat random too.