I wonder if it had something to do with them installing new brake pads they morning? I drove it 2 1/2 hrs home and it never came back on. Knock on wood
Sounds like you need an ABS capable Scantool
http://www.toyota-4runner.org/4th-gen-t4rs/151487-check-engine-trac-vsc-read-me.html
Would have seen OBDII DTCs if it set an MIL also.
The fact that it came on while you were test driving makes me think that the seller knew about it, reset it, and was hoping it wouldn't come on during the selling process. Walk away, this is no coincidence.