The Terminatrix's ability was "forming complex machines," not necessarily just controlling machines. In order to drive a car remotely, all she'd need to do is send some of her nanobots into the car where they could form the machinery required to move the steering wheel, manipulate the throttle, etc. I'm still not convinced that she'd make machinery to pull the gas pedal down rather than just adjusting the throttle from the engine compartment -- not to mention that she could never have enough leverage from within the steering column to pull the transmission lever down -- but at this point I'm just nitpicking. I know better than most that "nobody likes a nitpick," so I'm declaring that my complaint with the movie is completely invalid, and apologize profusely to the film's creators for my mistake.
That said, in her comment explaining this, aerospace brought to my attention another complaint I once had, about which I had completely forgotten. In the "Terminator" universe, the abilities of the Terminators get better and better as technology in the future progresses. But they inexplicably send the new upgraded Terminators back in time to a point AFTER the failed previous attempts. The logical thing to do would be to keep going after Sarah Connor EARLIER in time, would it not? Why keep trying forward in the time line when you know she's going to be expecting it?
Remember how in "Terminator 3" the Terminatrix could control electronics, enabling her to use them as an extension of herself? Remember how when it came to vehicles they'd do the David Fincher zoom-through down to the circuit level, showing that she's taking control of it only to zoom back out and show the shift knob move by itself, the gas pedal depress to the floor and the steering wheel turn by itself? That bugged the crap out of me. For me it was exactly like in "The Never-ending Story" when Sebastian got to the part in the book where Sebastian got to the part in the book. ("That's IMPOSSIBLE!" Both his response and mine. Luckily he was all alone in his school's attic; I was in a crowded theater and got simultaneously 'shhhhh'd and snickered at.)
Compare with the film "Maximum Overdrive." Shift knobs move by themselves, steering wheels turn without assistance, and gas pedals depress to the floor, seemingly without any cause. This was perfectly acceptable. AWESOME, in fact. I'm not entirely sure what the difference between these two examples is, but I suspect it to be the explanation of how it is working. In "Maximum Overdrive," there really is no explanation. For all we know, there are invisible beings sitting at the wheels of the vehicles. We know that an alien race is using Earth's machinery to "sweep out all the roaches," (those roaches are us) but there's absolutely no attempt to explain it. In "Terminator 3," on the other hand, they go out of their way to explain it, even using flashy graphics of electrons following circuitry. The problem, though, is that electronics don't work that way. I could buy the steering wheel, since most modern cars have "power steering," but the shift knob? There's no machinery for the electronics to activate to get them to move. To me that was just plain stupid and it spoiled the whole movie.
Do these types of things bother other people, or is it just me? None of the other unrealistic things in the film -- time-travel, cybernetic organisms, Claire Danes -- bothered me in the slightest, while such an inconsequential thing completely ruined it? Is that a normal human response?