2007 Pontiac Vibe P0121 Repair with a question at

Well I had my Daughter in-law car to fix this holiday. They drove up for Christmas with no issues. they started to drive to her mothers house and the car would not move, very fast. She called Asked some questions. she press on the throttle and the car would not hardly move, I asked if the engine light was flashing and she said no. She was on her why back to my house. I hooked up my scanner and it has a P0121 circuit "A" Circuit Performance code. I go to look for freeze from data and can not find it. I should say I tried looking in GEN OBDII, Pontiac Vibe, and USA Toyota Matrix. the scanner would only see the engine Model under Toyota and GEN OBDII.
So no freeze frame DATA to look at. I ran the car and did not see why it through that code. Read a little on that code and decided to erase the code and drive the car to see if it come right back. It did not. so I asked her to drive it and see if it come back and it did. Night had came and it was Christmas eve day. The next day Monday I hooked the scanner back up and looked for freeze frame again, did not find it. So I looked on BBB Industries web site for a wiring diagram, did not find it. the TPS has 6 wires. so then I looked on my Snap on Vantage and there it was. I tested the ground the 5v reference and the A & B Circuits. The two circuits had two different voltages. one was 0.8v at idle and the other 2.6v at idle. I still did not know what trips the code. I looked on-line some more and found info and found a Web page yourmechanic.com and it says.
What cause the P0121 code?
The TPS sensor circuit A learned range output to the ECM went above the specified voltage difference between the TPS sensor circuit B by more them 1.2v
The TPS sensor circuit A learned range output to the ECM went below the specified voltage difference between the TPS sensor circuit B by more them 0.8v

So looking at what I have seeing that the TPS and the ECM are reading the same. and tested for grounds and the ground wire. I replaced the Throttle body / TPS at $159.99. the car relearned its idle. I dove it around, she drove it around town before they left on there 3 hour trip home. No issues and they made it home.

I can see how hard it is to say lets buy this part and to be sure its right.
I retested the remained TPS and it did not read any different at idle or at higher RPM's. I did not see a dropout ether.

My question is why are the two circuits not closer in voltage?

Most manufacturers run 2 TPS sensors, and both voltage scales will be different. One sensor may start at .5 at idle and end at 4.5 WOT and the second may start at 4.5 at idle and .5 at WOT.

They do this so the computer can use an algorithm to verify the readings between the sensors. I believe it's a double redundancy check. One sensor vs the other. If either waver outside of a predetermined threshold from the other a fault is set. It's a failsafe manufacturers employ to prevent unintended acceleration. Especially in drive by wire systems.

It's difficult if not impossible to catch these faults with out a scope. You have to watch both traces and look for an anomaly. Sounds like you did the proper research and checks and made a good call.

Working on heavy trucks for a living I've seen the TPS sensors fail pretty frequently and almost of the TS for them from the manufacturers just has you ohm out wires, check for power and verify the TPS reading in the OEM scan tool. If all that checks out swap the part.

It's bs in my book, I get criticized for pulling out my Verus in a truck shop by my less knowledgeable colleagues but I'm not satisfied without knowing 100% that I'm making the right call.