I did find a bulletin that sheds some light on a possible issue, it is included below. Another concern that may affect operation, is whether or not anything has been spilled in the area, like coffee or soda for example. There also may be the possibility that, if anything is determined a failure and is part of a floor shift control, often times these are only available as a unit, no serviceable parts.
Bulletin No: 06-07-30-026
Date: September 26, 2006
Difficult to Move Shift Lever Out of Park/Delayed BTSI Solenoid Disengagement (Educate Customer/Replace Shifter)
2006 Buick Lucerne
2005 Cadillac DeVille
2006 Cadillac DTS
with Floor Mounted Shifter
Before replacing any components, please educate the customer as described below. The original shifter in this vehicle operates as it was intended. This design may not meet all customer expectations of operation. Replace the shifter ONLY if the customer wishes to have a new shifter installed and only after being educated about the design and operation of the shifter in the vehicle.
Some customers may comment that it is difficult to move the shift lever out of Park. On a second attempt, the shifter moves freely and functions normally.
The BTSI (Brake Transmission Shifter Interlock) locking bolt may not have sufficient time to unlock the shifter before the operator attempts to shift out of Park. Before replacing any components, please educate the customer as described below. The original shifter in this vehicle operates as it was intended. This design may not meet all customer expectations of operation. Replace the shifter ONLY if the customer wishes to have a new shifter installed and only after being educated about the design and operation of the shifter in the vehicle.
Customer Education and Expectations
The floor shifter in the Buick Lucerne and Cadillac DTS was designed for silent and smooth operation with a quality feel. A locking bolt keeps the shifter locked in PARK until the moment the brake pedal is stepped on. As soon as the brake pedal is pressed, a motor withdraws the bolt and allows the operator to move the shifter out of PARK. Some customers have a tendency to reach for the shifter AS they depress the brake pedal. This action does not allow the system enough time to unlock the shifter and traps the bolt so it cannot be withdrawn. The total time required to unlock from the moment the brake pedal is depressed is less than 7/10ths of a second. This short period of time is designed into the shifter so that when the brake pedal is depressed, the locking bolt doesn't produce a "clunk" due to such rapid withdrawal.
If the customer attempts a shift out of PARK quicker than the system can unlock the shifter, they merely have to let the shifter relax to the PARK position and then try again. They do not need to re-apply the brakes. These operating characteristics are normal and do not indicate any need for service. Once the proper operation of the shifter is understood, the customer may find it easier to use.
If after this explanation the customer still has concerns with the operation of the shifter, the dealer may replace the shifter assembly with a service unit that has the motor enabled to run at full speed.
Replace the floor shifter assembly. Refer to Floor Shifter Replacement in SI.
Shifters in stock currently have had the BTSI unlock motor enabled to run at full speed, minimizing any delay time in shifter functioning.
Wednesday, March 30th, 2011 AT 4:29 AM