I can't catch a break on the weekends these days. Which makes me glad I'm retired, but "for Pete's sake", every weekend a new problem with the family's cars seems to arrive at my doorstep. This time my daughter's Highlander flagged a "Check Engine" light and a "VSC" (Vehicle Stability Control) light while driving home from work last evening.
This morning I drove the car around the neighborhood and it definitely had an ignition miss. I then pulled the codes and found a P0306 - misfire (cyl. 6 misfire) and did the usual test by checking plug conditions and swapping coils between cylinders 4 and 6. Sure enough, after swapping coils between cylinders 4 and 6 the misfire moved to cylinder 4 -- bad coil. An easy fix with a new coil. Good to go!
The VSC problem was a brain teaser though. Long story short, after many other tests, the culprit turned out to be a faulty gas cap. Yup, a faulty gas cap set off the Vehicle Stability Control light. After doing some research, it turns out that Toyotas are notorious for indicating VSC issues even when there is no logical reason(s) for an actual VSC fault. The ECM controlled VSC logic must be very broadly defined to indicate a fault even when non-VSC subsystems are out of range.
Bottom line is that a VSC indicator light on a Toyota is a very strange event that could easily pull you down the diagnostic "rabbit hole", and potentially load the "Parts Cannon" with unnecessary repairs.
This is definitely something Toyota owners should be aware of -