OK, first off sorry for all the confusion I caused. Looks like my typing was faster than my thinking.
Looking a bit closer at the hardware side...

PIN C12 (GRAY): This pin is labled not used. Internally it tracks from the gray connector to an input network that defaults it low. The state of the pin is available through the PRU in port C bit 4. I will look at S/W to see how/if it is used.

PIN C11 (GRAY): This pin is labled TRACTION CONTROL SYSTEM ACTIVE SIGNAL. This pin is defaulted to ignition voltage and tracks to an input network (default high). The state of the pin is available through the PRU in port A bit 0. I will look at S/W to see how/if it is used.

PIN A23 (RED): This pin is labled TRACTION CONTROL SYSTEM SPARK RETARD REQUEST. This pin is defaulted to ignition voltage and tracks to a schmitt trigger receive curcuit. The input is used by the TPU only (TPU pin 22). We can only look at the inputs and outputs to the TPU and uses educated guesses about what is going on inside. Lots of work needed here to gain an understanding.

The first post on this topic should have named pin A23 as the source instead of C12. Swap these two references and I believe the post is corrected.

-Tom