For starters, reference this bulletin. See if it helps.
#07-07-30-032C: Shifter Binds, Ignition Key Sticks, Shift to Park Message Displayed On Driver Information Center (DIC), Dead Battery (Adjust Shift Linkage) - (Jan 8, 2010)
Subject: Shifter Binds, Ignition Key Sticks,"Shift to Park" Message Displayed On Driver Information Center (DIC), Dead Battery (Adjust Shift Linkage)
Models: 2007-2009 Cadillac STS-V, SRX
2007-2010 Cadillac STS
2006-2010 Cadillac CTS Sedan
2009-2010 Cadillac CTS-V
2010 Cadillac CTS Sport Wagon
Equipped with Automatic Transmission
This bulletin is being revised to add model years. Please discard Corporate Bulletin Number 07-07-30-032B (Section 07 -- Transmission/Transaxle).
Some customers may comment on one or more of the following conditions:
" The shifter binds when putting the vehicle into gear or park.
" The ignition key sticks or is hard to remove from the ignition lock cylinder.
" The "Shift to Park" message is constantly displayed on the Driver Information Center (DIC) when the shifter is in the "Park" position.
" A dead battery that follows after parking the vehicle for an extended period of time (less than 24 hours). This vehicle may have been left in accessory mode with the "Shift to Park" message displayed.
" The shifter binds when moving the lever from Drive to Manual mode.
This condition may be caused by the shift linkage adjustment, a slow Brake Transmission Shift Interlock (BTSI) mechanism or a Park Confirmation micro-switch that is not closed.
Adjust the automatic shift linkage following the steps below.
Verify the customer's concern.
Position the shift lever into the PARK position.
Check for any stored diagnostic trouble codes (DTCs). If any codes are set, diagnose the DTCs first using SI.
Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle in SI.
Adjust the automatic shift control linkage. Refer to Shift Control Linkage Adjustment in SI.
Lower the vehicle.
If the "Shift to Park" message is displayed, try wiggling or "bumping" the shifter while in the PARK position. If the message goes out, then repeat the adjustment. This is typically an indicator that the shift linkage is biased rearward. If the initial condition was Drive to Tap Mode binding, then the shifter linkage was initially biased forward.
Determine if the condition has been corrected. If the condition still exists, the automatic transmission shift control may need to be replaced. Refer to Automatic Transmission Control Replacement in SI.
Shift Control Linkage Adjustment
Position the shift lever in PARK.
Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle.
Notice: Refer to Fastener Notice in the Preface section.
Loosen the shift control linkage adjustment nut to allow the adjuster to slide freely.
Hold the selector lever on transmission against the rear stop to eliminate any play.
Tighten the shift control linkage adjustment nut to 9 N m (80 lb in).
Lower the vehicle.
Inspect the operation of the starting system with the shift lever in each position. The engine should only crank when the lever is in the PARK or NEUTRAL position.
If the key is stuck or hard to remove from the lock cylinder or there is a high button effort, the linkage may not be adjusted properly. Re-adjust as necessary.
Wednesday, January 18th, 2017 AT 12:05 AM