Thanks for posting the picture
Wow I learned a thing or two. I spent a good morning scratching my head over this schematic and try to figure out why there is a chassis ground vs. earth ground.
Then it hit me: Radio Shielding! So the yellow wire going in is earth ground. Notice that all the coils are connect to the earth ground. This is the same ground as the negative terminal in the battery. So the energy is flowing from ground into the coils and towards the potential (signal). Now see the dotted loop around the signal wires (chassis ground). This forms an EMF shield from the high energy being created on the spark side. I am willing to bet that the chassis ground goes through an RC circuit to filter out the spark plug noise.
Please do not power off, firmware update pending.....
2010AveoLT (03-09-2015)