The HEAD relay is operated when a ground is applied by the HRLY lead. This occurs when either the high or low beams are active. When the DRL's should be on, the ground is removed and 12v is applied, which makes the HEAD relay release.
The DIM lead has a ground applied when the high beams are on, or the DRL's should be on. The circuit is open when the low beams are on. This is the signal you were measuring on Pin #2 of DRL #2.
Since you see the voltages changing on pin #2 of DRL #2, we know that there are no broken wires causing the problem.
Originally Posted by Legioona
Thus, it appears that the problem is rooted inside the ECU?
I think you have the answer. Perhaps you should have a second look at turning on the DRL's with the Techstream application. If the DRL's are indeed turned on in the app, all I can think of is that your ECM has a different version of firmware, and that doesn't seem likely, but hey, it's Toyota.
If you really want DRL's you could use a couple of additional relays to apply ground to the DIM lead whenever the ignition was on, and headlights were not on.