7g-tronic Auxiliary Oil Pump problem?

[Welshey]

Has anyone else here ever seen fault code U1138 - CAN communication with component ‘Auxiliary Oil Pump’?

The car has the engine light on and feels low on power, 65mph is about all it’ll do uphill on the motorway. The gearbox often refuses to respond to manual inputs or won’t shift above 5th. Other times it’ll go up to 7th.

The MB specialist garage I took it to said they’ve never seen this fault before.

 

[steveq]

I can't help with the fault but I have removed the auxiliary pump previously. It has to be removed to access the TC drain plug on a 7g+ gearbox.
As far as I know, the auxiliary oil pump maintains oil pressure in the gearbox when the engine is off in stop/start mode.
It is just bolted onto the underside if the gearbox with 3 bolts and an electrical connector.

Very easy to remove but ATF will come out when it is removed. It will be much easier to do it as part of a gearbox service.

Here is a picture of what it looks like:-
Genuine Mercedes Auxiliary Oil Pump Gearbox 722.9(Start-Stop)OEM A2222700201 new | eBay

 

[steveq]

I can't help with the fault but I have removed the auxiliary pump previously. It has to be removed to access the TC drain plug on a 7g+ gearbox.
As far as I know, the auxiliary oil pump maintains oil pressure in the gearbox when the engine is off in stop/start mode.
It is just bolted onto the underside if the gearbox with 3 bolts and an electrical connector.

Very easy to remove but ATF will come out when it is removed. It will be much easier to do it as part of a gearbox service.

Here is a picture of what it looks like:-
Genuine Mercedes Auxiliary Oil Pump Gearbox 722.9(Start-Stop)OEM A2222700201 new | eBay

 

[MBenzUser]

I have read these pumps can get clogged and fail without a code being thrown. Any thoughts on how that would present and how eco start/stop would be affected?
What does maintaining oil pressure when the engine is stopped do outside of helping ease change gears as you accelerate.

I am having an issue where the car intermittently won't start from an eco stop. Have explored all the common electrical issues. No xentry codes.

 

[Petrol Pete]

Without oil pressure nothing in the valve body of the gearbox will work , so when the engine stops the gearbox 'stops' . That's fine when you stop the engine to park your car but when a car has stop/start it has to spring into life and take off immediately so ATF pressure has to be maintained in the transmission to make this possible .

I am sure it is way more complicated than that (why make thing simple ..right ?) but that is the gist of it .

 

[MBenzUser]

But does diminished ATF pressure prevent the engine from restarting (e.g. too much resistance since the car is in D) when it does an ECO stops or just leads to rough shifting once you start moving?
Also, how does this start/stop situation really differ from someone who turns the car ON and just starts driving right away? The oil pressure hasn't presumably built up yet either.

 

[Petrol Pete]

Not quite. 'Normal' auto box , foot on brake , start engine , move selector from park to drive = plenty of time for pressure to build and the car was in park (or neutral ) so nothing required of the transmission If in drive or reverse the engine will not start.

On stop/start the car shuts itself down while in gear (stopped in traffic) and is expected to move the instant the driver applies throttle and instant engine start up , not fish around selecting 1st or 2nd (depending on driver mode selected) . Again , probably more complicated than that.

It's only my humble opinion but I think start/stop is more trouble than it's worth and no one will ever convince me that stopping and starting any piece of machinery unnecessarily is a good thing (in the long run) for that piece of machinery.