The dreaded CEL / VSC / TRAC light trio lit up on my rig tonight, thankfully after holiday travel. Drove it yesterday without those lights and without issue. Fired it up and drove it down the driveway after they lit up this evening, again without issue. No detectable missing, strange sounds, misbehavior, even after switching into 4LO. I have had a rattle above my muffler, which stops when pressing the muffler up. As all hangers look to be in good order, it may be a loose heat shielding issue that I've yet to diagnose.
After reading a variety of threads related to these lights and gas caps, this thread by BlackWorksInc has been extremely helpful for this rookie:
Check Engine, TRAC, AND/OR VSC On? Read Me! - Toyota 4Runner Forum - Largest 4Runner Forum. I like the idea of knowing the source of the problem before clearing the codes via battery disconnect. So a code scanner's now at the top o' the shopping list.
One question for y'all: I just did a TPMS bypass within the past few days. Is there any chance this splice might have triggered this issue?
Thanks for your input and suggestions!