transmission changing upshift points

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Stuart O

Active Member
Apr 26, 2008
C 250cdi est.
Recently drove for 100 + miles in almost monsoon conditions from Inverness to Lochgilphead - I noticed after a while that the the auto box wasn't changing down as normal and was staying in a gear higher than normal :confused: - would the slippery conditions have triggered something in the g/box - it only lasted for approx 5 miles then reverted to normal, roads were awash / flooded at this point and at the time I only had about 20 psi in o/side rear, this was unknown to me at the time - found a nail in tyre later on the journey - car was loaded to the gunnels also, roof box full of golf gear :eek:

any genius's on here shed some light on this ??
car is 05 ML 270 W163
auto box changedown points ..

anybody here have any opinions / thoughts ?? it hasnt done it since that time, would water somehow have affected a switch somewhere ??

If the "symptom" went away after you increased th OS tyre pressure, then yes, that's the answer.

The ESP communicates with the TCM (Transmission controller) via the CAN lines and a change in the rolling radius of one wheel on the driveline will cause a message from the ESP on the CAN bus that there may be a traction issue, the TCM will respond accordingly with a change in the current shift strategy, in some cases you may experience higher gear starts (2nd even though the S/W switch is in the S postion) and inhibited kickdown function.

A period of soft or aggressive driving will also cause a change in the current shift profile as the system is adaptive to both wear and tear and driving style. HTH.
Like above, ESP may have detected that you are cornering or you have some wheel slip from deep water and it then asks the tranny to suspend gear shifts if possible because a gear shift may add instability at critical situations. At least it may have been just normal.
thanks guys - I was q happy that the car was trying to look after me but its the first time I have felt the effect of modern ESP etc etc.. q impressed !

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