Toyota's stock is probably undervalued to begin with because of the stupid pedal thing, and this probably makes it extreme. Short-term traders need not apply, though.
In principle, the two do not necessarily have to move in lockstep. However, because of the massive size, prominence, and stability of Toyota, one would ordinarily expect them to correlate extraordinarily heavily as anything else is an exploitable arbitrage opportunity.
and of course you can also do regular pairs trading (if they drift farther apart).