Look for a CO SEA-CHI full fare (e.g. Y8) and you'll see the routing. If the routing numbers are the same (in your case Routing 6), then it'll apply to your cheaper fare.
FYI:
Code:
ROUTING 6 FROM SEA-CO-PDX-CO-
OR FROM SEA-CO-LAS/PHX/SLC-CO-
VIA DTT-CO-
OR VIA HOU-CO-ATL/BNA/CLE/CMH/DFW/
IND/MKC/MSY/SDF/STL/FLL/MEM/ORL/RIC/
TPA/DAY/BHM/CRW-CO-
OR VIA MSP-CO-
OR VIA HOU-CO-
TO EWR-CO-CHI*
OR TO CLE-CO-DTT-CO-CHI*
OR TO MSP-CO-CHI*