Codes P2101 and P1516, engine goes into reduced power?

Hello, if you have tried another throttle body and have the same exact issue, its most likely going to be a wiring problem or possibly a failed ECM, but we will go with the wiring issue to begin with, do you have a multimeter to do some testing with?
And with the key Off, can you see if the throttle plates are fully closed with the air intake boot off? Do not put your figures anywhere near the throttle plates.

I do have a multimeter. I did test and verified I had 5 volts coming from the ECM but that is all I did. Was not sure how to do anything beyond that. I will look to see if the throttle plates are fully closed with the key off. But shouldn't they be if the key is off? I'll do that now.

Yes they should be. But that's one of the testing inspection steps, I'll post the rest here for you in a second. The 5v Ref is just the throttle position sensor, this code is for the actual throttle actuator, the motor that moves the throttle plates.

This is the code setting criteria that has been met to set these two codes, so the desired and actual position do not meet. It sets the codes and disables the throttle body.

It looks to be fully closed.

Okay, so, you verified the 5v Ref already, did you check to see what the Signal wire is reading with the key on as well? To also verify the Ground wire is good, you can recheck the 5v Ref using the sensor ground and Battery negative if you haven't already done that.

Actually I don't think it is fully closed. I got a better shot. I also compared it to the scrap one I bought. The scrap throttle body does look closed. But this one does not seem to be? See the updated picture.

Thats with the key Off I assume, yeah that doesn't look closed, can you unplug the throttle body connector pretty easy? And with the used one, you would need to clear the codes first before it may start to function, but I'm posting the flow chart for the P1516 below anyway.
This testing is first checking the voltage levels for the two wires that control the throttle body motor, and then checking the circuit from the ECM connector to the throttle body wires to see if there is high resistance, open circuit, short to ground, etc.
It's the X2 ECM connector, so I'll find that for you, but you can do the first step to determine which step is next after that.

Yes, I can remove the throttle body connector. I checked 5v ref with battery ground and it was 5v. I checked Signal with key on and it was 12v.

Do you think I should try the scrap throttle body I have? Also...clear the codes. I do have an ODB scanner and when I try to clear the codes from it, it gives a "failure". It would not clear them no matter what I tried. So, what I did was disconnect the batter for over 10min. Would that be sufficient to clear the codes?

Going back to the wire diagram you sent. I didn't catch it but there is no blue/white wire. I read it as brown/white. Actually, there is only 1 wire that has any white and that is the brown/white wire. This is the wire diagram I found.

Okay, your throttle body has 6 wires on it, there are two different designs for this year, one has a TPS with 2 signal wires, the other only has 1 TPS signal wire.

Okay, hang on, I missed your previous message about the 12-volts on the TPS signal wire. You can try the used TB, I'm wondering if the TPS signal wire is shorted to battery power now, can you check the TPS signal wire with it plugged in and see if you're still reading 12v, we might have to unplug the ECM X2 connector and recheck that signal wire again, I don't think there should be any 12v on it, unless that's a circuit integrity check, but sounds odd to me. This is the 6 wire TB or 5 wire?

The diagram you posted matches the 6 wire TB wiring I have. But I'm having trouble finding the OEM diagram with 6 wires, there's a change in the build for this year, causing this confusion. This is the OEM I'm seeing so far.

Let me recheck the voltage on the signal. I do have 6 wires.

Okay, I found the correct ECM X2 connector pinout for you at least, it shows 2 TPS signal wires.

Okay, actually. What would be the "signal" wire?

This is the 6 wire TB pinout, TPS signal 1 (D) brown/green and signal 2 (F) brown/blue. With two signal wires one may go up and the other down when pressing the throttle, some work opposite like that, but it should still only be 0-5v.

Okay, so, with the car "on", but engine "off". The voltage on the brown/green or brown/blue should go up and down. Probably opposite of each other?

Sometimes they have them that way, in either case, both signal wires should vary between 0-5-volts. With a code stored though, the ECM may not move the throttle plate at all.

My concern is more about the 12v reading.

I could not find 12v again. I might have made a mistake. I took more carful measurements now - now with the correct wire colors. Ignition "on", car "off". na means I was reading around 7-8mV. Super small.

BN/WH - na
YE - .8v
BK/BN - na
BN/GN - na
BN/RD - 5v
BN/BU - 4.9v

That's with the connector unplugged I assume? And this is with the new TB or used one?

Yes, unplugged and the old TB. I don't have any wire piercing probes. I think I should try the used again? With the old one not fully closed it seems that is wrong.

And disconnecting the battery is good enough to clear the codes?

Another question. Should I be able to move the plate around with my fingers (out of the car) to a fully open/horizontal position? The old TB I can move but it only moves a bit, and it doesn't seem to fully close unless I push it fully closed, then it bounces back to the partial open. The new (used scrap TB) I cannot move at. No matter how hard I push on either side it doesn't move. But it is fully closed.

You can back probe the connector wires with T pins or back probing pins if you have them, I'm looking up the information on a battery disconnect for this vehicle, disconnecting batteries is not like the old days, and this vehicle might have a smaller aux battery for Onstar options or Stop/Start system. Plus, there can be procedures that need to be done after a battery disconnect such as idle relearn, along with having a battery current sensor on the negative battery terminal. Some of those have a nut on them that can be a one-time use. So, clearing the codes with a scan tool is really the correct way to do it. What scan tool do you have? Is it just a code reader? I just don't want to see you disconnect the battery and end up with other issues.

It's called an "Ancel AD310 Classic Enhanced Universal OBD II Scanner"

Pretty sure the original TB is broken. There is a rattle when I shake it coming from it. Must be a spring that broke that fully closes it? I can easily open the plate to full open on the original TB. The scrap TB no way...too tight. Can't move it open at all.

No it's not a good idea to move the throttle plates by hand, these new electronic throttle bodies should be opened with a scan tool. When cleaning the throttle bore and plates I always open the throttle plate with either a scan tool or have someone sit in the vehicle with the key on and press the throttle down to open it, I know some people will open them by hand, but in some cases that can damage the internal components. The new ones are very complex, you may have two bad TBs, if the used one doesn't function with the key On, and came from a used parts lot, who knows how long it's been there or if it got water inside. This is really where a good scan tool comes in, that way you can monitor what the ECM is seeing for voltage signals on the TPS and throttle actuator.

Sounds like they are both broken, the used one sounds like it seized up.

So my best bet would be getting a new TB from GM. I just need to be able to clear the codes so it can do a relearn?

Once you get the codes cleared, you can follow this throttle relearn procedure, this is the non-scan tool procedure to be done if the throttle body is cleaned or replaced. Can you read live engine data with the key "on" with that scan tool? The communications from the data link connector looks to go through the body control module then to the ECM. But at least you weren't reading any voltages on the TB wiring, you may try checking the yellow wire and the brown/white wire each (with the key Off) for any shorts to ground, but it sounds like the original TB was actually physically broken inside, with stuff bouncing around inside.

I purchased a new throttle body, was able to clear the codes using the scan tool, and then ran through idle learn procedure you posted. It's been 3 days, and the car is running great. Thanks!

That's great news, really happy to hear things worked out well for you. Keep us in mind for future issues.