The VSC sensor is an accelerometer/yaw sensor - it is tied to the ABS system as well as the engine. When the sensor detects a shift in the vehicle body vs what the wheel sensors are saying, then it assumes the car is sliding - cuts engine power briefly and applies the brakes on the wheel that will pull the car back on track. Kind of works like traction control - but traction control is more interested in lateral acceleration changes (ie. straight line traction). ABS is the opposite end of the spectrum - also deals with lateral acceleration under braking. VSC and EBC work together to deal with everything else.
Still kind of weird for the light to come on - I know in Scions and Prius - they got the light to come on and stay on via shorting of pins in the dignostic connector. If the VSC is off - then the ABS is disabled as well. Might need to take this in to a Toyota dealership and have them take a peek. If they can find out what is wrong - it will be well worth the $85 diagnostic charge vs tossing darts at it. They would also be able to find out if any damage was done to the ECM (static discharge?) during the previous service. Might go a long way in getting you some compensation if they other shop fried the ECM.
2002 Corolla S, Silverstream, 1.8L 1ZZ-FE (VVT-i)
2003 Matrix XRS, Cosmic Blue, 1.8L 2ZZ-GE (VVTL-i) - RIP
2009 Matrix XRS, Blue Streak, 2.4L 2AZ-FE (VVT-i)
