2010 C5 Exclusive Reluctant to Change Up a Gear

[Ricksta]

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

[mooseshaver]

I don't think it is normal. I think if driven gently mine will go into 6th at around 42mph. It depends on hills and things. At 60 it's always in 6th when cruising.

[Mandrake]

Holding onto 2nd gear when in drive and not changing up to 3rd sounds very similar to the problem horsedentist was having with his C5:

Part 1:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=42277" onclick="window.open(this.href);return false;

Part 2:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=42691" onclick="window.open(this.href);return false;

The summary of these threads is that it was caused by different diameter tires on the front and rear of the car! The different front/rear speed signals were somehow confusing the ABS/ESP system which in turn was telling the gearbox to hold the gear and not change up to 3rd unless he manually overrode it. As soon as he fitted the same size tires front and rear the problem was solved.

[horsedentist]

Holding onto 2nd gear when in drive and not changing up to 3rd sounds very similar to the problem horsedentist was having with his C5:

Part 1:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=42277" onclick="window.open(this.href);return false;

Part 2:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=42691" onclick="window.open(this.href);return false;

The summary of these threads is that it was caused by different diameter tires on the front and rear of the car! The different front/rear speed signals were somehow confusing the ABS/ESP system which in turn was telling the gearbox to hold the gear and not change up to 3rd unless he manually overrode it. As soon as he fitted the same size tires front and rear the problem was solved.

Spot on there runs like a dream now.

Basically I came to the conclusion that it was a speed conflict between the abs system speed signal and the rpm signal at the gear box ecu , due to the wrong size tyre the car was getting a conflict ie: the gearbox thought it was time to change but the abs was telling it the vehicle speed was less than it should be so it was holding in gear.
The higher the speed the greater the percentage discrepancy on the speed sensors.
So at low speeds it was only a small percentage out so changed gear, at higher vehicle speeds the percentage was around 8% which was enough to over ride the ecu.
The car gets it's vehicle speed value from the rear abs sensors and mine was throwing an engine torque fault under the abs now it is fixed no torque fault, so I think the two systems are entwined.
Not insinuating you have put wrong tyres on but rear abs system may be worth checking?
Eric

[Ricksta]

Thanks for the suggestion. I have different branded tyres front and rear but the same size. The holding second gear problem has occurred when making a right hand turn. So definitely seems to be a connection there. But what about the reluctance to enter sixth gear? Could this be related?

[DickieG]

Is the car not still under warranty?

[mooseshaver]

On occasions mine redlines in second gear, I put it down to my work shoes not letting me feel how much I am pressing the accelerator. It does it in sport mode or when flooring. It can take a few moments to change up after it thinks I wanted sporty driving but I am now being gentle.
I haven't worked out the perfect way to drive for smoothness or even fast exits out if junctions, then my wheels just lose traction. I have all new Michelin primacy 3s. They are not winter tyres.

[Ricksta]

The car is still under warranty for a few more months. Problem is the dealer says it is working fine, I know it's not. I just tested it again, there is a particular intersection where I pull out turning right and the road then continues with a slight right hand curve - it pretty consistently red-lines 2nd on this corner. Elsewhere turning right isn't a problem. Does anyone have the specs on when it should engage 6th gear. I pretty consistently have to push it to >110K to get into 6th. I am sure that couple of weeks ago it would slip into 6th at about 70-80k.

[Xantippa]

My 2.0 HDi changes sixth gear at around 80km/h. Change from sixth to fifth gear happens around 65km/h.

[Ricksta]

Just reporting back on this one. It was the tyres as suggested - thanks. Although they appeared to be the same size, they were different brands and obviously had a slightly different profile or something.

[Mandrake]

Were the rear tyres bigger or smaller than the front to trigger the problem ?

When I was measuring the ride height on my Xantia recently I checked the rolling radius of the front and rear tyres, both 205/60/15 but different brands, and the rear tyres were 20mm larger in diameter than the fronts despite the fronts being brand new... So there can be a big difference between brands.