2007 159JTD Transmission 2nd to 3rd change over revs and changes with a bang

[Alfatz]

My 2007 159JTD Transmission 2nd to 3rd gear change over revs and changes with a bang. I believe this is a known fault with the transmission parts being under engineered . Can anyone point me in the right direction without the repairs costing as much as the car value.

[sidmann]

get the car transmission ecu scanned for fault codes. detailed fault is not stored in the engine ecu.
i had a problem with mine and it showed up as one of the pressure solenoid fault on the valve body.
after doing some research and know exactly which solenoid it was i started to open it up in tending to remove the vale body/solenoid assembly.

started undoing the solenoid wiring connectors and it takes a bit of prying with a small screw driver to release the lock and i noticed the one solenoid that showed up on the fault code came out freely with out any force. the connector wasn't seated in and locked correctly.
put it all back and refill new fluid, no problems since.