Auto gearbox issues on 2006 B-Class 170

johnny7

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Hi,

I own a B170SE 5-door Auto CVT, Petrol. It recently started playing up when going uphill, like it's struggling to choose the correct gear and after a few hours of driving will report "Transmission failure - visit workshop" on the dashboard. Over time, it's become progressively worse and now the fault shows up after a few mins of driving and the car goes into a single gear in limp mode.

I've had two mechanics plug it into a computer and assess the fault code to be due to a faulty ECU. Apparently this is a common problem on the A and B class.

I took it back to a mechanic who knows someone who can repair the ECU and, upon inspection, told me the gearbox itself is completely knackered - the oil is like water. He doubts the ECU repair would work and is advising a gearbox rebuild for £2500 + extra if the ECU still shows a fault after that.

I'm slightly confused but not really getting answers to my questions. Can you help?

- Does watery oil really mean the gearbox must be knackered and need a full rebuild?
- Wouldn't a fault code appear on the above if that was the case?
- Why wouldn't they test the ECU first independently of the vehicle and repair that to see if it solves the problem?

I'm not an expert here so looking for some validation of what I'm hearing and also if anyone has experienced this problem or knows what the answers to the above are, or what questions I should be asking.

Any help is appreciated! Thanks.
 

Steve@Avantgarde

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CVT oil is very thin in viscosity, the fact the gearbox does drive occasionally before the electronics put it into limp would suggest on face value the internals are ok, stranges noises and slipping would condemn the box in my view and whilst I have seen some CVT box failures on MB's and it cannot be ruled out, the valve bodies do fail and I have done about 10 and are the common failure.

Im not sure if any of these friends or experts are MB specialists, know these cars intimately or even have STAR diagnosis? If not, then find a Merc specialist who can help.

There are 3 Indies in Nottingham all with a good rep, whether thats close enough for you im not sure? Diagnosis is pretty straight forward with the aid of STAR and you will get the right diagnosis and opinion at an Indie.
 
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johnny7

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Thanks for the advice. When you say "slipping", it's not popping out of gear while driving. When the car reports the fault, if the car comes to a complete halt and then you accelerate, it takes a few seconds to respond and then suddenly jerks very aggressively into gear (whether forward or reverse).

If the ecu is reported as faulty by STAR, is it possible there are other faults with the gearbox that are not being reported? Or is the single fault code appearing pretty conclusive?

Thanks!
 

Steve@Avantgarde

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Depends on the fault code but I would like to think if that is what STAR is reporting and the guy operating STAR knows his onions then its more than likely the ECU.
 

Sotonian

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ECU problems

Here is a response I gave to another member with a similar ECU problem. I'm spreading it around to try and help others:-

I had the same message with my B200 CDi 2006, given much the same price, told that the new ECU had to come from Stuttgart and would only work in my car.

Happily, I found out from a friend in the Car Repair business, that there exist a few companies who specialise in the repair of faulty ECUs. I had my local Merc mechanic take out the faulty ECU, sent it to this company http://www.ecutesting.com/ they got it early Wednesday morning and by the Saturday morning, I had it back repaired. That cost £195 + VAT, the taking it off and refitting, effectively the transmission service including oil and gaskets, cost about £330, so about £560 in all.

The car has been driving beautifully this past week.

I suspect that this is too late for you, but I wished to pass on this info to others faced with the similar dilemma. I see Mercedes' attempt to extort large sums of money from their clients as a restriction of trade. It should be that we could take parts like this from car-breakers and recycle them. But having their faulty part repaired with a lifetime guarantee at a reasonable price is a good alternative and one which Mercedes would no doubt like kept quiet about.
 

Some guy on the internet

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Sotonian,

This thread has been dormant for 18 months.

Do you work for ecutesting.com?

All of your posts plug them.
 
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Frontstep

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You could have a point Sherlock, :)
 

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