C5 2001 2.2 hdi Auto sticks in second gear. FIXED

[horsedentist]

Well finally solved the gear change problem!

The car had 2 new tyres on the rear when I bought it, I was looking at it yesterday I suddenly realised the new tyres on the rear were 215-70-15 the ones on the front were 205-60-15. Took 2 wheels off the dead C5 I have here and put them on and hey presto car now changes gear!!!!!

According to tyre calculator on the net there would have been an 8.8% deficit between the actual speed and the speed signal sent by the abs sensors to the ecu which I presume would account for the engine torque fault reading on the abs ecu.

Any way I can stop banging my head on the wall now

[oneday]

i thought 215 and 205 were the width of the tyre and it would be the 70 that would make that sort of differance. im probably wrong

[horsedentist]

Sorry typo the fronts are 205-60-15

You are correct my friend.

Eric

[oneday]

now it makes sense to me

[horsedentist]

now it makes sense to me

I have spent bloomin weeks trying to sort the problem, cleaned all the abs sensors and connectors,cleaned all the gearbox connectors grovelled underneath it topping up gearbox fluid never thought to look at the tyres (had the damn things off once as well). Was convinced it was electrical because occasionally it would work for a while and then stop working and it worked ok on motorway with cruse control on and worked fine in manual. Then yesterday was just looking at the car as you do and suddenly the light came on so to speak and I thought "those new tyres look different" so checked the size, Doh.

[oneday]

it happens to us all at times we dont see the obvious still you got it sorted now makes xmas better

[Mandrake]

Ah brilliant, I'm glad you got to the bottom of it and your gearbox turned out to be ok.

I'm a bit puzzled about how it was causing the problem but I guess the ESP system must have been confused by the front and rear road speed signals being too different, which was then making it think the car was in an unstable state and inhibit the gear change. Did you re-enable the ESP settings in the gearbox ECU ?

[horsedentist]

Ah brilliant, I'm glad you got to the bottom of it and your gearbox turned out to be ok.

I'm a bit puzzled about how it was causing the problem but I guess the ESP system must have been confused by the front and rear road speed signals being too different, which was then making it think the car was in an unstable state and inhibit the gear change. Did you re-enable the ESP settings in the gearbox ECU ?

Yep esp is back on it. I am not sure what it was doing to the ecu but I kept getting an engine torque regulator fault on the injection and abs ecu's so must have been something to do with the speed readings. Anyway as you say changing the wheels has fixed it so who's counting as they say

I read a ZF manual which had a diagram of how and why it changes gear and the ECU is programmed with a graph and when the speed and rpm coincide in a certain curve it will trigger a change, so if the speed reading was incorrect and not allowing the two to coincide at the point that it was programmed for the rpm and speed to coincide, presumably it was not achieving the correct curve so the ECU was not seeing a point at which to trigger a change. As the % difference would be greater as the speed increased I think the curve was not far out at low speed hence the first change was ok but then as the speed increased the points on the curve became too far adrift to match the change point.

Only my theory.

And I haven't got a clue what I'm talking about, ask my wife

[Xantidote]

That's good news, and the explanation of the ecu getting conflicting information from the slower rear wheel rotation sounds plausible to me. Well done - sorted in the end. I guess the tyre sizing is something many of us would miss.

You said a month back that the car was a winter project, but I imagine you're getting it pretty well with it now

[horsedentist]

That's good news, and the explanation of the ecu getting conflicting information from the slower rear wheel rotation sounds plausible to me. Well done - sorted in the end. I guess the tyre sizing is something many of us would miss.

You said a month back that the car was a winter project, but I imagine you're getting it pretty well with it now

Just about there now need to change the down stream temp sensor on the cat and the temp sensor on the climate control and she is done the work got brought forward some what by the failure of the timing belt on the other one. Shame as it was a one owner 72,000 on the clock just got it all sorted and 13 months MOT and the belt failed a week later, still got plenty of spares now