Tyre Pressures, again! (1 Viewer)

[mapman]

Sorry Tigger -Tim just read post 24

 

[Driventemple]

As I mentioned in the Malvern thread. I will be there with the Multicuscan software and adaptors.

 

[dennis45]

Our TPMS dash light has been coming on intermittently. Usually followed by message TPMS not available. Only done 2k miles and had one sensor replaced back in May. Still keeps recurring. Took it to Fiat Professional today and they find both front tyres were 5bar rather than 5.5 bar and that raising pressures should solve the problem. Given the intermittent nature of the problem I am not totally convinced (and like others find such high pressures give a poor ride) but we will see. They have kept the vehicle over night and will road test again tomorrow.
2019 Base vehicle 2020 plate
Question: On the Fiat should there be an indication which tyre's pressure is wrong, ( my car shows all 4 tyres and there pressures on screen) or is it just a single warning light to check all 4? I suspect the latter but would like confirmation. Thanks

'TPMS unavailable' usually means that the TPMS module has lost contact with a sensor due either to the sensor not waking up or transmitting too weakly to be heard.
A low pressure alert is different (on Ducato, Peugeot and Citroen systems alike as they are the same module) and is always accompanied by a message such as 'Front right tyre low pressure 3.4 bar'.
Raising the pressure may give the impression of fixing the problem as a rapid rise or fall in pressure is one of the conditions that will wake a Schrader GG4 sensor, cause it to transmit and to stay awake for 20 minutes. But it will be the action of raising the pressure that has appeared to solve the 'TPMS unavailable' problem rather than the pressure to which the tyre was raised - and the problem will likely re-occur once the sensor goes back to sleep.

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[mapman]

'TPMS unavailable' usually means that the TPMS module has lost contact with a sensor due either to the sensor not waking up or transmitting too weakly to be heard.
A low pressure alert is different (on Ducato, Peugeot and Citroen systems alike as they are the same module) and is always accompanied by a message such as 'Front right tyre low pressure 3.4 bar'.
Raising the pressure may give the impression of fixing the problem as a rapid rise or fall in pressure is one of the conditions that will wake a Schrader GG4 sensor, cause it to transmit and to stay awake for 20 minutes. But it will be the action of raising the pressure that has appeared to solve the 'TPMS unavailable' problem rather than the pressure to which the tyre was raised - and the problem will likely re-occur once the sensor goes back to sleep.

Thanks, that’s very useful. It gives me plenty to discuss when I pick up the motorhome. We never got any tyre specific messages. Always either just a light or the light plus TPMS unavailable.

 

[Scattycat]

Some members may have seen, in another post, that I had replied to MMM’s article on the importance of maintaining the required tyre pressures according to axle loadings. I asked if they could comment on the fact that Peugeot and FIAT fit a TPMS that is set to 80psi. On my vehicle Continental’s recommenced settings are 59psi front and 64psi rear. Setting to these pressures triggers the TPMS giving warning messages and illuminating the dashboard warning light. Running 80psi, some 15 - 20psi over pressure gives a very harsh ride.

I had been trying to find a way to have the TPMS reset to reflect the correct pressures, without success.

I have now had a full reply from MMM which only compounds the issue, reproduced below.
it is long, and technical, but illustrates the stupidity of the lack of co-operation between base vehicle builders and motorhome converters.

Read it if you are affected and interested, otherwise feel free to move on to something more exciting.


Please forgive the delay in getting back to you.
Upon receipt of your query, we have been looking into this, contacting manufacturers and asking questions in the after-market. The outcome of this is not encouraging.

We had a reply from Peugeot and they stated that they set the TPMS thresholds at the factory and these form part of the homologation process. These can be set to different levels at the factory if requested to do so by the converter and this change is covered by their homologation process. It seems that if the vehicle is converted in the UK, the settings can be changed by the dealers if they are supported by appropriate final homologation documents from the converter.

What did we learn from this?

That the dealers have the ability to do the change but they are prevented from doing so by Peugeot. If there is any hope of getting this done it would require the converter to instigate it. I think we have to conclude that this is not going to happen.

I have asked a couple of high street tyre businesses and have been told the same thing. They cannot change the thresholds and their diagnostic units have only the ability to 'clone' an existing tpms valve to a new one if needed.

I have looked at this from another point of view. We asked Fiat (as the majority player in the market) and they have not replied at all but using my diagnostic system (Multi-ECUScan) i have been able to deduce that the TPMS is controlled by the Body Computer, or CAN -bus system. There is an option to disable the TPMS and run what is called a 'Proxi-alignment' afterwards that will convince the ECU that TPMS is not present. This would prevent any under or over pressure warnings along with the TPMS warning light illuminating on start-up. Doing this would be contrary to the homologation of the vehicle and in theory render the vehicle not roadworthy. In reality though, the only people that would ever know this would be an MOT tester and since only cars and other passenger vehicles have TPMS as a mandatory fitment; they would not be looking for it anyway.

The Multi-ECUscan device only works on Fiat vehicles and Peugeot have a different main ECU, so i can't know for sure how this would work but the body computers are almost identical to the Fiat ones so any diagnostic that can access the CAN-bus on a Peugeot Boxer should be able to disable the TPMS just as easily. I have spoken to a local Peugeot specialist and he said that he uses Lexia3 which is the Peugeot specific equipment and is certain that he could do as i can with Fiats but he is unsure whether the vehicle would reset to factory defaults when re-started or if the battery is swapped. We definitely need a guines pig vehicle to try it out on!

Failing the above, there are only two other choices available. Live with the warning being on and have with you documentation from the tyre supplier to confirm the reasons for the warning light being on if you are challenged, or follow the advice that i found on YouTube today that showed the TPMS sensors being removed and placed in a sealed container, pressurised to the correct pressure and then being stowed in the vehicle to fool the computer into thinking all is present and correct!

In either of the above, an aftermarket TPMS system could be employed to make sure that you can show diligence and that you are monitoring the pressures indepenently of the on board systems. In the case of the former, you would just have to alter the tyre pressures before an MOT test to ensure that the light is off at that time.

I will be preparing a full and detailed item for the magazine shortly. I will be advising buyers to avoid the option of TPMS entirely while it is not mandatory. Or perhaps insisting that the converter gets the TPMS set at a more reasonable value during the homologation process.

It is surprising that the manufacturers have chosen to use this form of TPMS (known as DIRECT, where TPMS sensors are installed in the wheels) as opposed to INDIRECT which is based on the relative rotational speed of the tyres, employing the ABS sensors. Indirect systems can be reset to whatever pressure you desire. I understand that Ford and BMW emply Direct systems in some of their cars and that these have a resettable feature for the owner; so it seems that a mixture of the benefits of both systems is possible but such decisions are made before manufacture, and cannot be changed.

This is a throny subject and i hope that the above is helpful in some way.

Regards

Nick Fisher
Tech Help Editor
MMM

I'm probably going to get shot down, but to me thwre us too much worry put on what the 'exact' tyre pressure should be based on axel weights at any given time.
Most of our motorhomes are based on commercial vehicles many of which are used as delivery vans, so they leave their depot fully loaded and return empty, do you think they adjust the tyre pressures as the load lightens?.
For motorhomes where the weight distribution is fairly stable each tyre manufacturer has their own suggested tyre pressures and I will use their figures as a starting point because I have found that sometimes the ride is still too hard or sometimes too soft for my liking and comfort and adjustment between +/- 0.5 bar makes little if any difference to the handling.
Okay, you can shoot me down now, but it's worked for me on all my vehicles over the years

 

[Jamesh]

Agreed

I'd suggest 50/60 for a 3.5t van and adjust from there.....

Cheers James

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[HugoBNB]

I have read with interest the many threads and posts relating to tyre pressures on the forum. We have had this, our first MH, 18 months now and set it up by the Adira book at 5.5 bar on all corners. We put air assist on the rear to increase the payload to 4100kg and kept the pressures the same. I have never been happy with the ride quality, nor the handling of the MH. So, after contacting Continental before this journey, I reset the pressures to 3.6 bar on the front and 5.5 bar on the rear. I kept the air assist at 3.2 bar. The difference in general ride and feel through the steering is remarkable. It feels much better to me.
Safe travels all.

 

[fat haggis]

Air seems a bit high. Try dropping that to 2.5bar

 

[HugoBNB]

Thanks, I will give that a go before we move off tomorrow.

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[HugoBNB]

Brilliant!
We are travelling a bit light so I dropped the air down to 2 bar. Much better again. When we are fully loaded for a trip I will take it up to 2.5 bar as you recommended.
Many thanks for your comment.
Safe travels

Air seems a bit high. Try dropping that to 2.5bar

 

[peterc10]

My 2015 Hymer based upon the Fiat X290 has Fiat's tyre pressure monitors as a factory fit extra. My Son bought (I paid for it!) some software which can, amongst many other things, access the Fiat ECU and reset the pressure settings both for cold and hot pressures. I can now run on Continental's recommended tyre pressures without getting any warning lights.