Automatic gearbox fault and wrong tyres

[Steveheidi]

Hi I have a similar problem to this below( post copied below, new to this sorry), I have been advised its a wrong a tyre confusing the ecu's on my C5 2010 plate, I have no fault codes at all and the car mechanic is a Peugeot/ Citroen trained. he had a similar problem with a car once and got to the point of replacing the whole box for a customer when he was advised to try the wheels of a new car ( same model, factory fitted wheels) and the gear box problem went way, never to return. so have been advised to change my whole set to pirelli tyres. happy to do this but wondering if there is a cheaper brand bit cheaper as its around £160 per tyre fitted ( kiwk fit, national tyres etc..) He also said which I feel is credit to the workshop, if I can live with it then wait till the tyres need changing as I have a lot of tread depth left. He went on to explain that the rolling resistance of this tyre then tricks the ecu into thinking I am climbing a hill so locks the gear to hold the torque
any advice pls...
Car details:- C5 2.0 HDI euro5 + vtr, tyre size 225/55/17/w
this is a post I copied below,

2010 C5 Exclusive Reluctant to Change Up a Gear





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Ricksta



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2010 C5 Exclusive Reluctant to Change Up a Gear








PostFri Feb 01, 2013 4:00 am

I have a 2010 C5 V6 Diesel with the 6speed auto gearbox. It has developed a quirky habit/fault. It seems to be reluctant to change up gears. Firstly it will occasional red-line 2nd gear before going into 3rd (but not always). Secondly it does not want to get into 6th gear until doing over 110Km/h. It is almost like it is in sports mode but not really. Sometimes it sails through the gears just like it used to, but more often than not it just feels different to how it used to feel. I have had the dealer check it and they say it is working normally.

Is it normal to cruise down the motorway at 100-105Km/h and stay in 5th and never go to 6th gear? This is a really had fault to demonstrate to the service centre as it is intermittent and just something that you know feels different about the car.

Has anyone seen a problem like this? Somewhere I thought that I saw a spec as to when it would change into 6th when in sports mode, that would at least give me a hint.

Cheers
Rick

[Trainman]

Hmm, this sounds vaguely familiar........ when the gearbox doesn't change up, have you tried pulling over and putting the lever into reverse? If so do you get like a double thump and then the car won't drive off in first?

I have a 6 speed auto box in the C6 and that can sometimes 'hold' first gear when it's cold but otherwise changes up through the gearbox with ease.

[Richard_C]

Sound a bit unlikely to me, assuming the tyre sizes are right for the car, but who knows. Mine is a manual.

As rolling resistance decreases with increased tyre pressure, within limits, maybe you could over inflate the tyres by 5 or 8 psi and do a test. If the problems goes away it might indicate a rolling resistance problem.

It would compromise ride quality and grip, but worth it for a few miles to try it out.

Some interesting stuff here, all tyres are US brands but the principles will apply|

http://www.nhtsa.gov/DOT/NHTSA/NVS/Vehi ... 0Center%20(VRTC" onclick="window.open(this.href);return false;)/ca/Tires/811154.pdf

See section 3.1.6, and in particular the top of page 44 provides guidance.

The new EU tyre labelling has a fuel efficiency category, in effect a proxy for rolling resistance. Look up your tyres on something like Blackcircles.com and see if they are unusual perhaps?

Moving away from tyres, I wonder if disconnecting the battery, having a cup,of coffee or two then reconnecting would make the ecu forget all it knows and relearn what is required. I know my old SAAB, which was an auto, had some sort of procedure to make the gearbox relearn, I think you did the battery disconnect and reconnect then ran through a series of accelerations up to a set engine speed locked in a particular gear. Long time ago though, forgot the details but it worked for me when the box decided to be harsh with its changes.

Those 2 things are free to try out, worth ago before buying a whole new set of tyres.

[Hell Razor5543]

I do recall that somebody else on the forum had an automatic C5 with mis-matched tyres (size wise), and it confused the ECUs (as they work out the speed from the ABS sensors). When they found the problem and fitted the correct size of tyres the ECUs were able to get a coherent speed reading and then managed the gearbox correctly.

[Trainman]

That's strange because the spare tyre on the C6 is a smaller size that the alloys, having said that it can be configured to run on 17" steel wheels, could the problem be that the configuration is set wrong?

[bobins]

so have been advised to change my whole set to pirelli tyres. happy to do this but wondering if there is a cheaper brand bit cheaper as its around £160 per tyre fitted ( kiwk fit, national tyres etc..)

Whilst views differ (hugely ! greatly !! widely !!!) on which are the best tyres for a car, if you're after a quality known brand tyre it's worth pointing out that Michelin are currently running a 'save on fuel' promotion when you buy some of their tyres. 4x 17" Michelin tyres will get you a £70 fuel card. Not all tyre garages are running the promotion so you definitely need to shop around. If you don't mind a little leg-work, Oponeo.co.uk are usually extremely cheap for supply only, then you need to find a tame tyre fitter who'll fit them for you for not much money. As a comparison, I got 4x Michelin Primacy3 225/55/17 97W supplied and fitted today (at Merityre) for slightly less (once the fuel voucher is taken into account) than I could get the tyres from Oponeo and then get them fitted locally.
Other cheaper ways to get tyres are places like Blackcircles.com mytyres.co.uk tyregiant.com tyreshopper.co.uk camskill.co.uk etc,etc.......

Also worth pointing out that Merityre will balance centreless wheels for those that have them !

[Mandrake]

I do recall that somebody else on the forum had an automatic C5 with mis-matched tyres (size wise), and it confused the ECUs (as they work out the speed from the ABS sensors). When they found the problem and fitted the correct size of tyres the ECUs were able to get a coherent speed reading and then managed the gearbox correctly.

Yes it was a C5 with mismatched tyre sizes confusing the ESP system.

On some models of C5 the ABS/ESP monitors all four wheel speeds and as well as using that for anti-lock purposes compares the different wheel speeds to determine whether the car is cornering hard or is about to enter a skid condition, under these conditions it will temporarily prevent the gearbox from changing gear to help maintain stability. (If you're in an "on the limit" cornering condition you really don't want the gearbox changing gear mid corner and suddenly changing the drive torque, perhaps putting you into a spin or skid)

The mismatched tyre sizes (even a few percent) can confuse the ESP system by giving different road speed readings for each wheel even when you're going in a straight line, causing it to enter this "gear holding" state when it shouldn't. I don't recall whether the tyre size mismatch was between front and rear tyres, or left and right however. The ideal situation of course is for all four tyres to have the same rolling radius, which is not guaranteed with different tyre brands even of the same "size" ratings...

[osx]

As for tyres, bought the Sailun Atrezzo ZS+ and I am quite satisfied. Done about 15k miles and tread is still 6-7mm so I guess they will last for at least another 15k miles. Haven't noticed any difference in noise levels compared to the Michelin's and Pirelli's and you can get almost 3 of them for the price of one Michelin!

[hattershaun]

Using the Lexia diagnostic computer you need to tell the car what size tyres are fitted to the car, in order to calibrate all the appropriate systems correctly, ESP, gearbox, suspension etc.
I've seen this being done on a friends X7 C5 tourer when the wheel size was changed from 18" to 17".

[Richard_C]

I got the impression from the original post that the tyres are the correct and standard size but the mechanic thinks the rolling resistance of that particular brand is the problem. Buying a whole new set of tyres seems an expensive way to test out the theory, you could do it and be back where you started hence the suggestion to fiddle with pressures first.

Unless of course the car was configured for another trim, Did some have 18 inch or even 19 inch rims? in which case a lexia session might sort it.

Would putting the vin number into service citroen show what it left the factory on or does it it not have that detail?

[Mandrake]

Rolling resistance is irrelevant, rolling radius of the wheels is important.

Also it's differences in the rolling radius of the individual wheels that causes the problem - if all the wheels are bigger or smaller by the same amount it doesn't matter.

If the front and rear wheels are different sizes, that's a problem. I would imagine mismatched wheels on the same axle would be even worse.

[addo]

Something is not right here in the original statements.

If there are such issues, unless there's a mechanical fault with the gearbox, there will be stored data. I'd suggest the car needs to be read with Lexia or Diagbox to determine better, the starting point.

[Steveheidi]

Hi just want to say thanks for all the replies and advice, I have had a automatic gearbox specialist look at the gear box, to which it is a mechanically sound gear box, nice smooth gear changes, no recorded faults at all he did point out it maybe a wheel sensor, ABS or speed sensor. I then took the car to a garage called the French Car Centre ( guess you can tell what cars they deal with) they plugged in the test gear and picked up no faults with these sensors, they did pick up an minor fault with the air circuit, was told its not a problem and not to get it fixed unless it becomes a fault. In regards to the wheels the front tyres are a different brand to the rear, I have also replaced only one tyre on the rear due to a puncture, didn't change the other as advised the tread is nearly new ( an honest tyre fitters!!) so any more advice would still be greatly received

[Mandrake]

So you have mismatched brand tyres on the rear axle ?

Measure the outer diameter of the two rear tyres and see if they differ significantly.

[Richard_C]

This looks far more likely than the original diagnosis of rolling resistance, which may well be a red herring.

Measuring diameter accurately is quite difficult but would show up any gross differences. You could try to measure the rolling circumference, either by string or tape or perhaps a chalk mark on tyre - roll car forwards one exact rotation and measure distance on the ground.

Far more accurate would be the manufacturers website. I don't know if they all do it, but I have just been on the Falken website, I have ZE914s on mine, and there is a technical data sheet with the rolling circumference of all the sizes and types.