W221 S class 2006 transmission issue

[traffic0703]

I have experienced problems with the transmission of my W221 S class today (7G Auto). The car had been on a 50 mile trip so fully hot.

Firstly, a jolt as coming to a stop (just before fully stop). It has done this before when cold but not hot.

Secondly, when in fully auto mode, I tried to accelerate out of a roundabout but no response to throttle input. Pressed all the way down to the kickdown switch but it would not change down to accelerate.

But when I used the manual mode buttons on steering wheel I was able to change gears normally up and down and the car also accelerated perfectly normally.

If you switch engine off and re start all problems cleared however they have come back again as above.

Electro plate was changed one year ago.

Any ideas what this may be please?

 

[John Laidlaw]

We're having a run on 7g 'boxes at the moment!
Needs a Star diagnostic I'm afraid - youre probably sick of hearing that. Strange the manual buttons are working but could be the ECU I guess....
I had the opposite on my SL, auto worked but manual flappy's didnt - tried everything and finally replacing the steering wheel module sorted it

 

[traffic0703]

Hi John,
I have booked into dealer for Star test.

They can't do that for nearly two weeks as busy. I am worried that it could be the valve body and therefore a very expensive repair.

I tried the car again tonight and no symptoms present at all.

In view of that, can anyone give me some reassurance that this is likely to be electrical/sensor related?

Same symptoms as when they changed the electroplate last year - this has a two year warranty. Unlikely a new Mercedes part would fail so soon?

 

[John Laidlaw]

2 weeks? Really....are you talking main dealer here? I would have thought your local friendly indy would be quicker and it needs checking. Where are you based by the way

 

[traffic0703]

yes main dealer. Based near Sheffield. I will be able to use other car so won't risk causing any problems.

 

[John Laidlaw]

Wise...

 

[Steve@Avantgarde]

Sounds more like an engine fault, if the gearbox had gone into limp mode then you wouldn't be able to use manual/tiptronic/paddles to override what the gearbox wants to do.

Might be something like a turbo actuator jam or inlet port shut off motor fault.

 

[traffic0703]

thanks. What about the jolt as the car slows to a stop - which I assume is the box going from 2 to 1?

Is it possible the symptoms of no performance are not related to this?

What I can't understand is if I used the paddles to select correct gear, engine performance was normal. If there was an engine fault wouldn't the problem still be there?

 

[Steve@Avantgarde]

The engine control module and gearbox control module are connected, the gearbox can be effected by what the engine does. If the engine is in the middle of trying to sort out a value it doesn't like, and you start pulling gears then it can come back to life and or go the other way and go to limp.

7G's have a characteristical jolt 2-1, my C320CDI does all the time, but also it can jolt on downshift again if the engine ECU is adjusting values from sensors that are incorrect.

Please know that, unless its a hard wire fault code like a lost signal, EML limp mode is always the last resort, the control electronics will always try and manage a situation first and if it cannot, then it will generate limp, but there is always an intervening period you will feel as the driver in that mean time. Of course, sporadic faults can occur as well, which will reset with the ignition.

That is why I never guess at what a fault might be without looking at the evidence of the fault codes first and from your description of the fault, it sounds like the engine has the issue, not your gearbox.

 

[traffic0703]

thanks very much for the info.
I will need to be patient until codes read.

 

[traffic0703]

Star test shows two faults:

inlet port shut off motor fault. (stored fault and failed under testing)
O2 Sensor (current fault)

I have authorised the 1st item but not sure whether to do the O2 sensor or not. Could the 1st item cause a fault code for the O2 sensor?

Any advice please?

 

[Steve@Avantgarde]

If the 02 is a current fault then the guided test to measure the resistance of the 02 sensor to confirm its operation will tell you if its goosed or not. It has no correlation to the IPS.

 

[traffic0703]

ok thanks Steve. They did say it has failed. They did not seem to be concerned that it had failed as I said fuel economy was good and no engine management light has come on.

I am concerned what other problems may be caused so will speak to them tomorrow for a quote for a new sensor.

 

[Steve@Avantgarde]

02 sensors wont bring on the EML light. It doesn't control the engines running, its more of a reporting sensor than a crucial running sensor.

They are £221 from MB but you can buy exactly the same Bosch unit from Euro for half that.

 

[traffic0703]

Is it something I ought to replace - I am a bit confused as thought it affected the fuel/air ratio?

 

[Botus]

Is it something I ought to replace - I am a bit confused as thought it affected the fuel/air ratio?

no idea on your car, but its quite common to have 2

a wideband one that controls the engine management and is critical and a second after the cat to inform if the proper one is doing a good job. The second is to protect the cat, not make the engine run right (that's the first one's job). the first one is in region of 100 quid the simple one 40 quid

 

[Steve@Avantgarde]

If you want your engine to run as optimally as it should then yes.