U0121 = Data bus, anti-lock brake system (ABS) control module - no communication
Set Condition:
The DTC will set if a valid CAN ID was not received in the from the ABS module
or The ECM/PCM doesn't receive a Bus Message from the Anti-lock Brake Module.

U0415 = Invalid data received - anti-lock brake system (ABS) control module
OR
U0415-Implausible data received from ABS
Set Condition:
When the TCM detects an incorrect CAN ID from the ABS control module.

U0402 = Invalid data received - transmission control module (TCM)
Set Condition:
An error message has been received over the bus from the Transmission Control Module (TCM).
OR
U0402–IMPLAUSIBLE DATA RECEIVED FROM TCM (FDCM)
Set Condition:
The Final Drive Control Module is receiving implausible data for gear or PRNDL position from the TCM
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What happened right before you got the codes? Battery go dead? Jump start?
Any recent Mods or changes you made?

Most of the above could be due to a chafed, loose, or burnt wire. If they are intermittent.
If they are continuous, then most likely your ABS module or PCM is shot, or there are other modules which are not correctly programmed. (VIN Missing/Mismatch, TIPM, battery or ignition related)

Make sure you have + and - to the ABS module.
Check fuses J6 and J7 are good and are seated correctly.
Black 47 way connector on the left inboard of the TIPM.
Check the following Pins.
Pin 1 (TN/RD wire) B+, Pin 13 (BK) -,
Pin 25 (DG/RD wire) B+, Pin 38 (BK wire) -.
Other then that you are looking at a dealer visit...

I had a similar error code problem that started intermittent but after a month abs,traction & airbag light turned solid, gave up and took to dealership, ABS module replaced $ 600 bill

Bummer!
The TIPM is the main junction point of the CAN "C" BUS.
So here is something you can try.
Disconnect the Neg(-) battery cable.
Disconnect the Pos (+) battery cable.
Disconnect the Pos (+) battery cable at the TIPM.

Release the TIPM retaining clips and roll the TIPM over.
Look for the "C1" connector. It is black 50 way. This is the one that has the CAN C bus connections on it. Release the locking arm carefully! It is not strong, and may break. You may have to wiggle the connector and pull on it while releasing the arm.

Look at Pins 15 and 16, 15 is WT/LB wire CAN -, 16 is WT/BK wire CAN +.
Check for corrosion in the plug and on the TIPM Pins. DO NOT insert anything into the plug wire holes! This will make them to big to make a good connection.

While looking at the TIPM, check the wires under there for chafing.
When I did my lift, I found a wire that was rubbing on my TIPM bracket. Luckily it was before it went all the way thru the insulation. In my case the wire was rubbing on the rear inboard side of the bracket... Anyway, check them out.
If it all looks good, put everything back in reverse order from above.
Good luck. I hope it is a simple chafed wire under there...

I'm out of ideas short of chasing wires or replacing modules one by one at this point.
There are tests that a dealer can run with their scanner. But the fault has to happen during the tests. If the tests turn out inconclusive, the manual has them run continuity tests from plug to plug on each module reporting the lost communication.
As you can imagine the costs of having them do this adds up real quickly.

I got a replacement off ebay and went to get it programmed but its come back as faulty showing a code for brake pressure switch as well as vin mismatch. So looks like sending it back and getting another one.

It will have a VIN missmatch until it is initialized. Not sure if the pressure switch error will correct once the ABS has the correct VIN.