I just bought a code scanner so I was trying to make sure it worked by causing the SES light to trip on purpose. I unplugged the IAT sensor two days ago, and the SES light never came on.. I figured it must not be THAT vital of a sensor (thus the no SES) so I then unplugged the MAF sensor. The car ran very poorly (barely at all) yet there was no SES light. I know the light works because it turns on when I turn the ignition on, but it doesn't while the engine is running.. The scanner showed no codes.
So my question is, just what DOES it take to trip this SES light if two semi-important sensors are unplugged and those don't even set it.