Follow the input wire to the TCU side of the C-101 connector on the fire wall, make a small cut lengthwise on the wire and voltage test from there to the TPS ground. The wire there is a straight shot from the TCU, so the only possible resistance or faulty contact is the plug at the TCU.
Might want to also test the voltage "in" for the three wire connector also, just for reference. The voltage in for the three pin connector, comes form the ECU and for the four pin connector from the TCU. About 90% sure I´m right, but it has been awhile since I picked my way through the harness.
Mine had a low input voltage that turned out to be WD-40 in the TPS connector, I tested for voltage on both sides of the TPS connector and was loosing a volt at the connector.
I use an Exacto knife, and make a small cut lengthwise in the wire, then seal it back up with a dab of silicon. Trying to get a good reliable contact for the meter leads, other ways, is iffy. I also run the TPS wires (both sets) over the top of the TB rubber intake elbow, makes testing really easy.
I doubt the TCU is putting out low voltage, but anything is possible. I scrubbed all the connectors at the TCU and ECU a couple of years ago. I did find a couple of contacts (pins) that had backed out of the holder, the locking tabs for the contacts (pins) aren't real reliable.
Sorry about the typos, my spell checker gets kind of pushy and doesn't know what a TPS is and keeps wanting to change it to a TAPS.
There is usually some resistance were the ground wires for both sides of the TPS, go through the TCU and the ECU (I've measured 2 of each and all had some resistance in the module for the ground circuit, but not much). I think there is some kind of primitive surge protection in the circuit. A reliable, fairly accurate digital meter is just about a must, to get good readings. Mine cost about $25 at Home Depot.