Code issues after transmission replacement? The P1603 and U0101 codes ?

What codes are they? It sounds like the fluid is low or you have an input shaft speed sensor that is not working.

here are two guides that can help with the location of the sensor in the images below:

https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid

and

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Check out the images (below). Let us know what happens and please upload pictures or videos of the problem so we can see what's going on.

Hi. I believe the speed sensors have been checked and Transmission fluid level is good.
I have a Bluetooth obi II scan which connects to my phone and the fault codes are...
P1603 - powertrain
U0101 - network

The network fault could be the main one as the powertrain fault only came up yesterday when I disconnected the battery.

Here is information on the codes:

P1603 code is a generic powertrain code that indicates a malfunction in the internal control module memory.

The U0101 code refers to a communication problem within the network of the vehicle.

So it seems like one of the main grounds was left off when the transmission works was done please double check the grounds around the transmission.

Hi, sorry for the late reply. I've had a back injury.
I have checked the main grounds, and they all seem to be in place. Tomorrow I will pick up a 2nd hand wiring harness so I can hopefully cancel that out over the coming days.

I am glad you are feeling better, back injuries are rough to say the least. Please let us know how it goes.