Actually, after doing some reading, the CEL, which Toyota calls the MIL (Malfunction Indicator Light) can illuminate for MANY things, many of them dealing with engine trouble, but some strictly on emissions. This is the lamp that ODB requires.
Then you have the triangle of doom, which is officially called the Master Warning Lamp. I have mistakenly been calling this lamp the MIL. This light usually illuminates for hybrid problems and non-engine related problems, but can come on for strictly engine problems too.