I got this e-mail from my Service Dept this morning. It's a little more descriptive.
This issue indicates that the IC thinks the ignition is off and is looking for the park detect input from the shifter on circuit CET52. If the engine is still running, this indicates that the IC is receiving the wrong network message from the SJB for ignition switch position.
If this issue is present when the vehicle is shut off but the IC is displaying the message even when the shifter is in park, refer to cell 37-1 of the wiring diagrams. The shifter grounds the circuit whenever the transmission is shifted to Park. If the circuit is open or the switch internal to the shifter is faulty, the IC will not see the correct input.
Jiggle the shifter when the concern is present to see if the message goes away. If it does, replace the shifter. If not, remove the IC and check pin 7 for ground. If no ground is present, trace the circuit and repair the open or replace the shifter as necessary. If ground is present, check for pinfit at the IC using the appropriate flex probe. If pinfit is good, reconnect and retest. If the message is still present, suspect and internal fault in the IC itself.