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The dipstick is intended for the workshop to check the oil level because there is a special sequence how the tranny fluid is checked. I can provide you with the order number of the dipstick and the instructions if you require them. First of all, the oil leve should be checked and replaced. When the oil change is done, experienced mechanic can tell if tranny is mechanically in order or not. According to the syptoms, it might be that the input and output shaft longditutual play is too big, so it must be checked without the removal of the tranny. There is a shim behind the propshaft flange which can solve the problem without dismatling tranny.
Another cause for bad shifting quality can be the engine's mass airflow (MAF) sensor.
I am afraid that generic scanner will have limited access to the transmission control unit. But it is worth the try. Also the trans fluid should be checked for coolant traces if the tranny radiator is integrated into coolant radiator. If the tranny radiator is separate, this test is not needed.
Thanks for the accept and best regards,
Theoretically it might be. I would still check the shim behind the propshaft output flange. It is not so often that there is absolutely no connection in D. The shim is very cheap, and nothing hard to replace it. Ask the workshop if they are willing to take the control unit back if it is not the cause. Sometimes the gasket at the transmssion starts to leak and the tranny oil gets into tranny ECU by wires. Very often in such cases, the cleaning of the ECU will solve its malfunction. Of course the gaskets at the tranny connector must be replaced first in such case as well. There are many things to be checked before throwing parts at the problem.
Let me know what has been done so far. Oil change? Any swarf present? Any coolant traces in the tranny oil if radiators are integrated? What are the fault codes in tranny CU? Any faults in Engine CU?