Could use some help understanding my scope waveform

2006 CHEVROLET SILVERADO 2500HD 6.0l gas LQ4. No DTCs stored. I graphed the throttle position sensors (1&2) because I have been having random stalling issues on this truck.
**WITHOUT THE FAULT OCCURING**
Throttle position sensor 1 drops to zero , throttle position sensor 2 does not. Throttle position sensor #1 5v ref drops to zero. Throttle position sensor #2 5v ref does not.
In my scope:
green: tps1
yellow: tps2
red: tps1 5v ref.
blue: tps2 5v ref.

Specifically, how do I know if the position sensor is bad or if the TAC module (mounted on the firewall of this truck) is faulty. I suspect the position sensor is shorting the 5v ref. down.

Also, why does it not set a code? I suspect it does not set a code due to happening 5 times per second and the condition for setting a code is shorted to ground for 1 sec.

I played around with this and if I unplug the throttle body connector, all the wires read a constant 5v (which really confused me because I did not expect that). Following the diag chart for P0120, it appears the signal should have 5v when unplugged.

Any thoughts on this would be helpful, thanks.

You may want to disconnect the 5V reference #1 terminal within the throttle body connector. Then jumper the 5 V #2 reference to this terminal. A shorted tps 1 would then pull down the ref 2 voltage.

With the connector unplugged you really get 5V on ALL wires, even the low reference/ground ones? If this is not the case and the 5V are present on the signal and reference wires only than it probably is a pull down sensor design.

I only have 5v @ both signal wires and both 5v reference wires with the connector unplugged. Low reference is 0 volts. Checked w/scope, no meter.
Ok. This is what I have done. I started over because I realized I was mistaken and tps2 is the problem, not tps1.

My trace colors are:
Yellow - position E on the connector - only labeled 5v, I assume for tps#2
Green - position F on the connector - tps#2
Blue - position G on the connector - tps#1
Red - position H on the connector - only labeled 5v, I assume for tps#1

First, I depinned terminal H and E and swapped the terminal positions (H&E are both 5v references for the throttle body). Doing this set a code and the reduced power message on the dash(could not clear, dead fault). I reswapped the terminals back to their original positions. No codes. Then I verified my results by doing it again. Same thing, set a code and reduced power message. With the throttle blade in default, my scope was fine, no dropping out 5v good, tps sensors both matched.

Second, I depinned and swapped H&E, F&G all at the same time. When I did this, the problem followed the wires/terminals. Thus, the red trace and blue trace showed the dropping out.

Third, I put all the terminals back to their proper position from factory. When I did this the problem followed the wires/terminals. The yellow and green traces showed the dropping out.


After the problem followed the wires, I scoped the low reference wires @ the throttle blade. They seemed fine/stayed @ 0v. Then I scoped the throttle blade motor terminals and it appears motor control 1 drops to zero as well. Motor control 2 stays constant @ 12v.

I retested with the throttle body unplugged. Motor control 1&2 show 5v, tps1&2 5v references show 5v. I reconnected but with the reduced power message, same thing. 5volts for all 4 wires mentioned. Once I cleared the code, then it was back to motor control 1 drops out like tps2 5v reference.

So, a module related issue or still a throttle body issue? Motor shorting out internally?

Earlier, I scoped the TAC module power and ground. If the module was unbolted from the firewall, it acted like no ground(12v) but with I bolted it to the firewall it has a good ground. Looking back, maybe I had a bad connection on the ground terminal for TAC module ground. Thus, I just rescoped power and ground to the TAC module. I even captured the truck stalling but unfortunately, my terminal probe was no good on the tac module power. I have to try to catch it happen again. When it did start and stall, it appeared the ground was good. Picture included. (blue= tac ground/ red-tac power(assumed bad connection)).

Side note, it has started and stalled twice today; both times it was when I unbolted the TAC module from the firewall. That said, I have tapped on the module (no change) and I left it unbolted and now the truck works fine again.

**edit**: Unless motor control 1 should be constant @ zero and the fact that it is 12v indicates a bad module ground and/or module?