S-class gearchange woes - any thoughts ?

[Cool Mart]

Ok, a small dilemma for you to ponder.

I have a W220 S-class with a gearbox fault, it’s not a terminal fault and the car is drivable, the best way I can describe it is that the gearbox seems unable to choose what gear to select as you approach junctions or roundabouts. It seems to change out of the current gear as I slow down but not engage the next gear until there has been a pause, it then engages with a thump. Now it doesn’t do it every time – maybe every 8th change is poor - and if I drive slowly it happens less. Also when I accelerate hard it occasionally revs between the gears before again engaging with a clunk. The gearbox fault code that comes up gives no more information than something along the lines of ‘intermittent loss of drive’ ? The gearbox performs the majority of changes without a problem so with my limited knowledge leads me to think it is most likely an electrical/sensor problem. The MAS has been replaced and also the ATF, both within the last 8 months. I don’t understand enough about the function of the speed sensors and the gearbox ECU, and certainly don’t want to change things on a whim – if it were a faulty speed sensor would it not show up on a fault code read ?

The car is currently with an independent who is well recommended by members of this board, but he also seems to be struggling to diagnose the problem. The independent has suggested a new valve body but this was replaced by another garage less than seven months ago (7000 miles), and to replace it again will cost iro £600 with no guarantee it will solve the problem. I have no problem spending money on the car but with a pregnant missus I can’t afford to waste money on it ! The last thing I want is to spend £1000 and then have to replace the gearbox anyway (anyone know how much a new S-class gearbox costs ?)

I’m really not sure which way to turn now … I can book it in to Mercedes but have a suspicion they will have less of an idea than the independent, and would probably take the easy option and want to fit a new gearbox.

What would you do ?

Thanks Mart

 

[BlackC55]

Is there a fault code and what is it?

Is the ATF level perfect?

 

[television]

To me the fault sounds exactly like what was being discussed here, that is the torque converter clutch.
When the TCC does not lock up the gearbox does not know what to do, it will flare when changing up and be in any gear when changing down often not being able to make up its mind as to what gear to be in

please read the thread I think that it fits the bill http://www.mbclub.co.uk/forums/showthread.php?t=42473

The TCC does not show up on diagnosis very well, it is operated by a electro hydraulic solenoid that in turn is driven by a pulse width modulated signal

 

[BlackC55]

It can be activated and deactivated with a Star to check if it works.

 

[C43AMG]

I had a similar problem. MB replaced the control unit £578 + £180 to fit it, under Service + warranty, fortunately.

 

[television]

I had a similar problem. MB replaced the control unit £578 + £180 to fit it, under Service + warranty, fortunately.

This unit is eletro hydraulic, and a missing signal from the ECU could cause this as in your case

 

[recycled]

oh dear not another auto problem

 

[television]

Cars built around 2000-2001 can have poor connections in the gearbox ECU this is a known fault by MB and in the service repair pages

 

[Brian WH]

I had a similar problem with my previous CLS with 7 speed box.

After a few visits to the dealer under warranty, they reprogrammed the ECU with the latest software and then set the gearbox to suit. That solved the problem when the gearbox got used to my style of driving after a week or two.

Talk to the dealer and the technician about this.

 

[Roger Jones]

Given the electronic complexities of today's systems, what I have to say may be completely irrelevant, but the symptoms as described are so consistent with the problem I had with my 1996 W124 E320 Coupé that I offer the information nonetheless. My problem was caused by a main dealer refilling the autobox with 2 litres less than it needed. That was part of a 36k service that cost me well over £600; I never went back.

 

[pc-uk007]

Hi Television, I have a 2001 s320 s class w220, that has a problem that cause gearbox to default to a higher gear when pulling away from stand still at times (limp home mode) this can be quickly rectified by switching off ignition and restarting car, no warning lights come on when fault happens, in your posting you stated connection problems gearbox ecu, what i would like to know where is ecu located and what i am i looking for ????? my gearbox gearchanges are ok and it appears to me a electical connection problem that i would like to check first before taking car in for dianostics.

 

[BlackC55]

TV has been banned from this site.

The gearbox control unit is in the passenger footwell inder the metal plate. I doubt connection issues though. Get it on a Star and I am sure there will be fault codes logged.