SLK 722.6 Auto Box losing drive

[Aston Dabb]

Got a 2003 SLK230 with a 722.6 Gearbox in it that is losing gears when it’s warm (reverse and drive). Gears are fine when cold but always loses drive as it warms up; it struggles to drop into gear from stationary after around 2 mins of running, but does manage to drop in, and after around 4-5 minutes; the gearbox has nothing but neutral and park! We’ve had the gearbox out a multiple times to try different things (we’ve even put a new wiring loom from the G/Box ECU to the Gearbox onto it!). Been told by somebody to ensure that the oil cooler isn’t blocked and I checked that by blowing compressed air down one pipe and seeing what came out the other pipe, which fresh gear oil came out due to it only just being replaced, and to make sure it had enough oil in it, which it had! We took the gearbox out prior to this to check that the gearbox oil pump was operating correctly as somebody had also suggested that we may have sheered the two metal pins off that drive the pump from the torque converter when we replaced the torque converter due to us first thinking that was the issue, but we hadn’t sheered them off and the pump was operating perfectly. The gearbox has absolutely 100% got the correct amount of oil in it and that was confirmed by an MB dipstick oil check from cold and MB dipstick oil check at 80 degrees Celsius (Temperature according to DAS). There are no faults related to gearbox in any modules. Is there anything else we could check?

 

[AMGeed]

What are you using to look for gearbox ECU fault codes?
I doubt a generic code reader is up to the job.
Has the electroplate been replaced?

I would find a good Mercedes indy and have the codes read using MB Star diagnostic equipment.
If you are losing gears then fault codes will be stored.

Where are you located in case someone can recommend a good indy.

 

[bembo449]

As above , star would have saved you a good amount of time and money with a pin point diagnostic, its not an unusual problem so im sure it can be sorted once you know for certain which part has failed

 

[LostKiwi]

What are you using to look for gearbox ECU fault codes?
I doubt a generic code reader is up to the job.
Has the electroplate been replaced?

I would find a good Mercedes indy and have the codes read using MB Star diagnostic equipment.
If you are losing gears then fault codes will be stored.

Where are you located in case someone can recommend a good indy.

I think that since he's referring to DAS he already has Star.
I can't remember if it's possible in Star but it would be useful to know the oil pressure from the pump (old school method of diagnostic). The symptoms you describe sound just like lost oil pressure.

 

[Aston Dabb]

What are you using to look for gearbox ECU fault codes?
I doubt a generic code reader is up to the job.
Has the electroplate been replaced?

I would find a good Mercedes indy and have the codes read using MB Star diagnostic equipment.
If you are losing gears then fault codes will be stored.

Where are you located in case someone can recommend a good indy.

@AMGeed @bembo449 I work for MB Truck & Van; I use their Star’s and I’ve ran it through DAS as mentioned about monitoring temperatures. None of us know the car side too well in Truck & Van and none of what i thought could’ve been up with the box has cured it? @LostKiwi the oil pump looks visually well when we took it apart and inspected it on Friday.. could it still be losing pressure?

 

[malcolm E53 AMG]

I know you haven’t seen any codes which you generally would do with an electric plate speed sensor fault but the symptoms do sound very much like it

 

[LostKiwi]

@AMGeed @bembo449 I work for MB Truck & Van; I use their Star’s and I’ve ran it through DAS as mentioned about monitoring temperatures. None of us know the car side too well in Truck & Van and none of what i thought could’ve been up with the box has cured it? @LostKiwi the oil pump looks visually well when we took it apart and inspected it on Friday.. could it still be losing pressure?

There could be an oil pressure leak internally in the box.
Old school diagnosis says measure the pressures in the box at various points so determine what's happening.
If oil pressure is good then look for mechanical issues.
Automatic gearboxes rely heavily on oil pressure to operate. No oil pressure, no drive.
Unfortunately the 722.6 has no pressure measurement ports.

 

[Aston Dabb]

I know you haven’t seen any codes which you generally would do with an electric plate speed sensor fault but the symptoms do sound very much like it

@malcolm210 Speed sensor was very first thing to be replaced