2009 Dodge Journey transmission

Hi I have a 2009 Dodge journey that won’t shift to second gear it stays at first gear. I took it to a mechanic who changed both the speed sensors and changed transmission fluids and engine. But the car now drives in first gear what could that mean??? Then the ! And the check engine light be flashing.

There is a critical fault detected by the Powertrain control module, the blinking check engine light indicates that you should not drive the vehicle, it should be towed. The computer faults will need to be reviewed to determine the cause of failure.