Tyre sensors

[KennyW]

I'm getting fed up with the very leaks from the valve assembly on my C5. I'm think of changing to the good old rubber valve.

To remove them, i'm thinking thefollowing:

1. Tyre of rim
2. remove sensor and valve from rim
3. replace with rubber valves

But how do you disable the system ?

Kenny

[GiveMeABreak]

The valve stem kits are quite cheap Kenny and are supposed to be fitted at each or near every tyre change. I had a persistent leak from one tyre and had it changed FOC. The valve stem kit is only about a £5 and will last for several tyre changes. The system does it's job well enough for me and has always been accurate so far - and I suppose if you think about it, they always replace the valves at tyre changes with rubber valve types fitted.

On another note, a faulty TPMS is now an automatic MOT fail on cars registered after 1 January 2012, so just for you to be aware - I can't remember what year your car is now Kenny.

[Paul-R]

Kenny - if your car is earlier than 2012 and you DO decide to replace them with standard valves I'd very much like the cast-offs! I'm looking for a set of TPMS valves for a spare set of wheels I'm putting together to hold winter tyres for my C5.

[KennyW]

Marc and Paul,

The car is 2010 and I have a spare set of TPMS in the garage. I have used a valve replacement kit on this tyre which has reduced the leak rate. But it is still an irritation. WHY on earth this should be MOT fail I don't understand when you should check tyre pressure, fluid levels regularly. I try to do this once a week.

Kenny

[GiveMeABreak]

It's just another bit of legislation they brought in - they say it saves fuel by having the correct tyre pressures (every 10% under inflation is 1% fuel loss). All tyres will leak air over time (not everyone is as regular at checking them as you Kenny) so serves as an early warning, plus there's the safety angle of driving on under-inflated tyres - which causes premature tyre failure or a puncture at worse, etc. accident reduction.. They brought this in for all new cars registered after 1st Jan 2012 - but doesn't apply retrospectively to older cars. PSA have been fitting them for over 15 years now. I know it doesn't warn you about idiots driving on bald tyres with the threads exposed, but I'm sure they'll think something up to cover that soon enough.

[Paul-R]

Kenny - PM sent.

[Richard_C]

It's just another bit of legislation they brought in - they say it saves fuel by having the correct tyre pressures (every 10% under inflation is 1% fuel loss)

Later Citroens (and some other marques) have abandoned the tyre pressure sensors, presumably because they were troublesome and the system cost them money. The new way to comply is to compare wheel rotation rates, I guess using the ABS sensors, and warn if one is different. When you fit new tyres there is a reset procedure so the system can tell what the normal rotation rates should be. We have a C3 with that system, 16000 miles and never a peep out of it and I am very happy to have avoided the era of pressure sensing valve stems.

The new way is helpful if one tyre deflates a little, but won't tell you if all 4 gently deflate at similar rates over time. It has a safety purpose but its hard to see how the new way of doing it helps fuel consumption.

Something of an aside, a few years back I picked up a hire car in the USA, must have been 90 degrees + a the airport and I guess Hertz check pressures before the cars go out. 2 days later, motel up at 11000 ft, just about zero when I started the car and there were four angry flashing beeping warning lights on the instrument panel. First reaction was one of 's..t it's broken' but calm reflection and some free air at a gas station put things right.

[GiveMeABreak]

That'll be Indirect (iTPMS) over the direct TPMS systems. Not as accurate as they don't measure tyre pressures, but are more customer friendly and of course CHEAP by comparison. They rely on the customer to inflate the tyres to the correct pressures to start with, then the system is reset by the driver, where a learning cycle is completed to compensate for roads, speeds and the like - so need anything up to 60 minutes before they are calibrated. It's a sign of the times, cheap and cheerful...

[dnsey]

So what happens if you park with one side of the car in the hot sun, and the other in the shade? Tyre pressures can be sigificantly different in such circumstances.

[DHallworth]

The torque to tighten the new sensors on the rim to is literally finger tight. Any tighter then this will distort the aluminium washer with the rubber seal underneath the rim and cause leaks... Ask me how I know!

David.

[GiveMeABreak]

So what happens if you park with one side of the car in the hot sun, and the other in the shade? Tyre pressures can be sigificantly different in such circumstances.

A very good point, it works using several types of info including the fact that deflated tyres are have a smaller diameter than a correctly inflated tyre. This is used by the car's speed sensors to make determinations. The later systems can monitor funder inflation simultaneously in all four wheels and use signal processing algorithms and advanced software to improve things further.