C5 tyre pressure sensors
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  1. #1
    1000+ Posts pottsy's Avatar
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    Default C5 tyre pressure sensors

    Here's one for the Brains Trust.

    Are these adjustable in any way?

    Why I ask is that the "factory spec" for my tyres is 36+ psi which, as far as I'm concerned, is way too high for normal motoring and probably even for highway work.

    My car has Chinese "Black Lion" tyres on it, not my choice, they were new on the car when I bought it last year.

    My experience from using these tyres on the Xantia (financial necessity, not choice) is that they're a fairly hard and unyielding sidewall, hence my desire to run them down around the low 30s or even 28/29 psi.

    I stress that this is NOT underinflated for these tyres and/or the weight and usage. They won't wear funny but will indeed provide a more comfortable ride around town, something a Citroen should always provide.

    So anyway, the damn things beep at me if there's anything much less than 35 psi in them and I have a moral objection to being dictated to by a Box of Binary Bits or even someone with a sliderule* and rolling resistance tables who's never driven the car.

    So can anyone tell me if they're adjustable? I'd love to be able to set them to a range between 28 and 38 psi, since being warned if they got below 28 would be acceptable.

    I can't find anything in a quick check with the Lexia, but I don't claim to be fully au fait with it's use or interpretation.

    So over to the BT.

    I look forward to being enlightened and/or disappointed in equal measure!

    Cheers, Pottsy

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  2. #2
    Real cars have hydraulics DoubleChevron's Avatar
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    doesn't work like that ... pressure doesn't matter, it's the pressure difference between tires. YOu can run any pressure in the tyres so long as there axle has the same pressure side to side.
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  3. #3
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    Quote Originally Posted by DoubleChevron View Post
    doesn't work like that ... pressure doesn't matter, it's the pressure difference between tires. YOu can run any pressure in the tyres so long as there axle has the same pressure side to side.
    Actually pressure does matter.

    Pottsy

    The monitor will compare the transmitted value (pressure and in some cases temperature as well) with preset values to determine if the tyres are within the desired operating range or not. If not then the alarm will be activated.

    Most systems will have a set value at which the alarm goes off. Some vehicles and systems have user adjustable threshold values which allow you to adjust the values to what you desire. This is common for 4X4 vehicles airing down in the sand.

    Most systems built in by the manufacturers will have preset values at which the alarm goes off. In that case you will need to go into the computer and alter the threshold settings for the alarms, not always a user friendly operation. Sometimes this is available via an onboard screen. Often it is not and you need to get in with an electronic scan tool. I am not sure if your C5 will allow for user adjustment via a menu.

    I suspect that you will need a Lexia to adjust the values or turn them off (which may be the easiest solution). Luckily my C5 does not have OEM monitors, but I have an aftermarket unit which allows for setting of the desired value.

    Quick Google found this thread
    French Car Forum ? View topic - C5 Tyre pressure sensors
    Hope this helps
    Peter
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  4. #4
    Now go make me a sandwich Hotrodelectric's Avatar
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    One mild suggestion, after reading Peter's comment: go ahead and decrease the pressures to where you think the tires will ride and drive wellfor you. Don't, however decrease them much further than the 28psi or so you mentioned. The sensors probably have a threshold quite a bit lower than that. Drive the car for a couple of KMs, and see what results on the monitor screen.

    The pressure monitor systems aren't far removed from any other idiot light. They only come on once some sort of disaster isn't far off, or a sensor has packed up.
    The measure of your character isn't what you do when people are watching- it's what you do when they aren't watching.

  5. #5
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    Well I had a deflating tyre on my C5 the weekend past.
    A stone had punctured the tread. Probably in my own driveway.
    At first it identified low pressure on the right hand rear tyre. I stopped and cast a calibrated eye at the offending tyre (Michelin Primacy).
    All looked good at this stage 5 min from home. At 10 mins I stop at a petrol station and the tyre is now obviously low on air.
    Check all other tyres to 36psi. Offending tyre to somewhere near 50.
    The car then tells me it has a puncture.! Oh and the STOP light will not go away!
    So, off to a tyre place to have a repair done.
    The system is obviously designed for idiots (me), you may have a better chance of defeating it Pottsy as you have a reasonable amount of mechanical / electrical smarts. I'd be looking at first principles. Are they purely electronic or is the sensor mechanical at its source?
    Still at the end of the day a $30 repair beats buying a new Michelin.

    You could buy a set of Michelins instead of Red Dragon, but that would hurt at the:
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  6. #6
    Fellow Frogger! dieselman's Avatar
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    Just turn them off via a Lexia.
    Leon

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  7. #7
    1000+ Posts George 1/8th's Avatar
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    Quote Originally Posted by dieselman View Post
    Just turn them off via a Lexia.
    Hi Leon, why the hell would you do that? A mate of mine is a mechanic and he told me a couple of days ago that these type pressure sensor systems are continually being retro-fitted at his work, and people are paying $600.00 and more for the privilege, yet here in the C5 it comes as a standard safety feature.
    It's apparently very popular with the 4WD people.
    cheers...

  8. #8
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    They do get confused if you move the wheels around.
    The actual sensors are rather more costly than $600 per set if you are buying them as spare parts. Remember, the neck is listed separately, so if someone damages just the neck, you may not have to replace the whole thing. The neck is much less costly than the whole unit.

  9. #9
    Now go make me a sandwich Hotrodelectric's Avatar
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    Quote Originally Posted by David S View Post
    They do get confused if you move the wheels around.
    The actual sensors are rather more costly than $600 per set if you are buying them as spare parts. Remember, the neck is listed separately, so if someone damages just the neck, you may not have to replace the whole thing. The neck is much less costly than the whole unit.
    My brother ran into that with his Ford Ranger. He fitted a nice set of aftermarket wheels, but decided to skip the TP sensors when he found they were 150.00/wheel. He still has the original wheels with the sensors, but they (the sensors) can't be fitted to the new wheels without spending lot of dollars just for the attaching bands.

    Jim went with the simplest, cheapest solution- he ignores the light.
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  10. #10
    1000+ Posts Greg C's Avatar
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    I have often thought that these things up the complexity of a vehicle for no real benefit. But then I guess all of us who drive real Citroens have at some stage come very close to destroying a tyre without really noticing. Especially on the rear of a D or CX. Maybe not a bad thing to have.
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  11. #11
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    They saved us on our last trip to Tassie. The sensor went off on the first day - back right. With 245/45 18s it was hard to even tell the tyre was at half pressure. I imagine had we continued driving on it it would have been well damaged by the time I realised there was something wrong.
    Craig K
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  12. #12
    1000+ Posts gerry freed's Avatar
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    If you had an accident here in France and the car was not equipped with the manufacturer's approved tyres at their approved pressure, you could have the book thrown at you. As I recall only certain Michelin and Continental tyres have OEM approval on the recent C5's
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  13. #13
    1000+ Posts pottsy's Avatar
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    I don't actually question the efficacy of the gadgets. They're one of those things that I've lived without for ever yet don't know how I ever managed without them. (Despite my constant laments on the way that cars are becoming too dependent on electronics, I put the desirability of pressure sensor alarms up there with central locking and remotely adjustable mirrors. )

    What I'm asking is are they adjustable, and the overall response seems to be that they're not.

    I think I'll spend some time determining the exact calibration by varying pressures at a controlled rate over a number of trips and see what the result is.

    As I said, I'd love for them to be set to something below about 28 psi or so as I could have a good ride yet still have the functionality of early warning of a slow (or even rapid) leak.

    Stay tuned for an exciting analysis!

    I can see another chart coming up!

    Cheers, and thanks for the input so far, Pottsy.
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  14. #14
    1000+ Posts George 1/8th's Avatar
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    Hey Pottsy, I don't think I'd really run my tyres as low as 28 psi. Your fuel consumption will go up for starters. Most cars use about 32 PSI I think...
    Wouldn't that be soft enough?
    Cheers... George 1/8th.
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  15. #15
    1000+ Posts pottsy's Avatar
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    George. my fuel consumption round town is not a significant factor. Being the diesel it's high 30s to 40s in old school mpg so I can yield a bit. For a highway trip I pump them up to the low 30s anyway.

    That being said, I'm slowly stepping the inflation up by a nominal 1psi at a time and appear to have hit on the right figure at 33psi.

    Once I inflated to 33, the alarm went away. That being said, it was a hot day so maybe it expanded to above the alarm threshold. I'm leaving it to see if a cold morning results in the alarm recurring at that figure.

    The research continues!

    Cheers, Pottsy
    Buvito Ergo Sum!

    The Fleet:

    2018 C3 Shine ("Oscar" Mrs P's)
    1974 D Special Manual Sedan ("Moby Dick")
    2006 C5 HDI Wagon Auto ("Mephistopheles")
    1982 2CV6 ("Gaston") On the road! (Woohoo!)
    1957 Slough 2CV ("Alphonse") Waiting in the wings
    1975 GS Pallas ("GiSelle") Also waiting in the wings
    And for Fun, 1968 Mini Deluxe ("The R & D'luxe" 1078cc, Grin Factor 100!)

  16. #16
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    The sensors on our 2006 C5 have saved us $$$ twice. Last time it started talking when the tyre pressure was 26 PSI .. not enough to damage a tyre.
    When I had a new set of tyres fitted and the tyre fitter moved the wheels from their original positions the sensors went wild. I returned to the dealership and was told " drive on, they will readjust to their positions after a couple of kilometres"..sure enough. The sensors calmed down. I still don't know if the wheel sensors are supposed to indicate just which tyre is low, or send out an investigation request. Either way THEY WORK !

  17. #17
    Real cars have hydraulics DoubleChevron's Avatar
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    Quote Originally Posted by Peter O View Post
    Actually pressure does matter.

    Pottsy

    The monitor will compare the transmitted value (pressure and in some cases temperature as well) with preset values to determine if the tyres are within the desired operating range or not. If not then the alarm will be activated.

    Most systems will have a set value at which the alarm goes off. Some vehicles and systems have user adjustable threshold values which allow you to adjust the values to what you desire. This is common for 4X4 vehicles airing down in the sand.

    Most systems built in by the manufacturers will have preset values at which the alarm goes off. In that case you will need to go into the computer and alter the threshold settings for the alarms, not always a user friendly operation. Sometimes this is available via an onboard screen. Often it is not and you need to get in with an electronic scan tool. I am not sure if your C5 will allow for user adjustment via a menu.

    I suspect that you will need a Lexia to adjust the values or turn them off (which may be the easiest solution). Luckily my C5 does not have OEM monitors, but I have an aftermarket unit which allows for setting of the desired value.

    Quick Google found this thread
    French Car Forum ? View topic - C5 Tyre pressure sensors
    Hope this helps
    That's interesting, my reading on the 407's annoying tire sensors was they just differentiated between each other, but didn't have a pressure threshold that would trip them (if all the other tires were equally flat).

    seeya,
    Shane L.
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    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

  18. #18
    WRB
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    On old British cars, the tyre sidewalls were quite tall which improved the comfort (one of the reasons Rolls Royce used Avon tyres). Of course, being cross ply, they would wonder all over the road....
    The warning only comes up on start up so, just ignore it. I used to run my C5 at 35psi

  19. #19
    WRB
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    i meant 33psi...

  20. #20
    1000+ Posts George 1/8th's Avatar
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    Quote Originally Posted by pottsy View Post
    George. my fuel consumption round town is not a significant factor. Being the diesel it's high 30s to 40s in old school mpg so I can yield a bit. For a highway trip I pump them up to the low 30s anyway.

    That being said, I'm slowly stepping the inflation up by a nominal 1psi at a time and appear to have hit on the right figure at 33psi.

    Once I inflated to 33, the alarm went away. That being said, it was a hot day so maybe it expanded to above the alarm threshold. I'm leaving it to see if a cold morning results in the alarm recurring at that figure.

    The research continues!

    Cheers, Pottsy
    Great work Pottsy, hopefully as a result of your diligent testing and research we might all get a better idea of what to expect...under different conditions.
    cheers... George 1/8th.

  21. #21
    1000+ Posts pottsy's Avatar
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    The story so far!

    I seem to have hit on an acceptable compromise of 32psi. The car still feels OK, and the annoying little beep and graphic have gone away for now.

    I thought I had it at 31 but once the weather cooled a bit, beep went the beeper!

    So far, so good at 32.

    Time will tell.

    Cheers, Pottsy
    Buvito Ergo Sum!

    The Fleet:

    2018 C3 Shine ("Oscar" Mrs P's)
    1974 D Special Manual Sedan ("Moby Dick")
    2006 C5 HDI Wagon Auto ("Mephistopheles")
    1982 2CV6 ("Gaston") On the road! (Woohoo!)
    1957 Slough 2CV ("Alphonse") Waiting in the wings
    1975 GS Pallas ("GiSelle") Also waiting in the wings
    And for Fun, 1968 Mini Deluxe ("The R & D'luxe" 1078cc, Grin Factor 100!)

  22. #22
    1000+ Posts Ken W's Avatar
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    The sensors on our C5X7 with 17" wheels seem to get active below 29psi. I did manage to get into the control system with the Lexia a few years ago when I replaced the steel spare (no sensor and with bong bong at the start of every drive when using) with a mag that had a sensor so I could log the new sensor into the system (see a previous post on this). I found that the system reads tyre rotation speed, temperature and pressure as well as battery condition and probably some other parameters. It looks to communicate via bluetooth or zigbee or some other MAC address based wireless protocol. The address on the sensor is in decimal but you have to enter into the system as hex so some maths is required. You can log about 8 wheels into the system so you have a set of summer and snow wheels. I don't remember seeing if you can adjust the alarm threshold.

    Cheers,

    Ken W

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