With no power to steering ,steering wheel can be moved about 2 in. in either direction

Question edited for clarity and dreadful spelling of 'Cadillac'.
Question moved to model category.

Yes it does have power steering.

https://www.google.com/search?q=2009+Cadillac+DTS+power+steering

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Which power steering system does your vehicle have ? EPS - electric power steering or hydraulic power steering . Do you have a EPS light lit on the instrument cluster ?

Power Steering System Description and Operation (EPS)
The power steering system reduces the amount of effort needed to steer the vehicle. The system uses the powertrain control module (PCM), body control module (BCM), power steering control module (PSCM), discrete battery voltage supply circuit, steering shaft torque sensor, steering wheel position sensor, power steering motor, driver information center (DIC), and the serial data circuit to perform the system functions. The PSCM and the power steering motor are serviced as an assembly and are serviced separately from the steering column assembly. The steering shaft torque sensor and the steering wheel position sensor are not serviced separately from each other or from the steering column assembly. The steering column assembly does not include the power steering motor and module assembly.

Power Steering System Description and Operation (HPS)
The hydraulic power steering pump is a constant displacement vane-type pump that provides hydraulic pressure and flow for the power steering gear. The hydraulic power steering pumps are either belt-driven or direct-drive, cam-driven.
The power steering fluid reservoir holds the power steering fluid and may be integral with the power steering pump or remotely located. The following locations are typical locations for the remote reservoir:
• Mounted to the front of the dash panel
• Mounted to the inner fender
• Mounted to a bracket on the engine
The 2 basic types of power steering gears are listed below:
• A recirculating ball system
• A rack and pinion system
In the recirculating ball system, a worm gear converts steering wheel movement to movement of a sector shaft. A pitman arm attached to the bottom of the sector shaft actually moves one tie rod and an intermediate rod move the other tie rod.
In the rack and pinion system, the rack and the pinion are the 2 components that convert steering wheel rotation to lateral movement. The steering shaft is attached to the pinion in the steering gear. The pinion rotates with the steering wheel. Gear teeth on the pinion mesh with the gear teeth on the rack. The rotating pinion moves the rack from side to side. The lateral action of the rack pushes and pulls the tie rods in order to change the direction of the vehicle's front wheels.
The power steering pressure hose connects the power steering pump union fitting to the power steering gear and allows pressurized power steering fluid to flow from the pump to the gear.
The power steering return hose returns fluid from the power steering gear back to the power steering fluid reservoir. The power steering return line may contain an integral fin-type or line-type power steering fluid cooler.
In a typical power steering system, a pump generates hydraulic pressure, causing fluid to flow, via the pressure hose, to the steering gear valve assembly. The steering gear valve assembly regulates the incoming fluid to the right and left chambers in order to assist in right and left turns.
Turning the steering wheel activates the valve assembly, which applies greater fluid pressure and flow to one side of the steering gear piston, and lower pressure and flow to the other side of the piston. The pressure assists the movement of the gear piston. Tie rods transfer this force to the front wheels, which turn the vehicle right or left.
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steering rack or gear . 2X2 - 4X4 engine . Depends on steering system .
When you turn the steering wheel, the steering gear rotates the pitman arm which forces the relay rod to one side. The tie rods connect to the relay rod with the ball studs. The tie rods transfer the steering force to the wheels. Use the tie rods in toe adjustments. The tie rods are adjustable. The pitman arm support the relay rod. The idler arm pivots on a support attached to the frame rail and the ball stud attaches to the relay rod.
The 2 tie rod are threaded into the tube and secured with jam nuts. Right and left hand threads are used in order to permit the adjustment of toe.

Binding linkage , steering gear worn etc....

Power Steering System Description and Operation (w/o Electro-Hydraulic Steering)
The hydraulic power steering pump is a constant displacement vane-type pump that provides hydraulic pressure and flow for the power steering gear. The hydraulic power steering pumps are either belt-driven or direct-drive, cam-driven.
The power steering fluid reservoir holds the power steering fluid and may be integral with the power steering pump or remotely located. The following locations are typical locations for the remote reservoir:
• Mounted to the front of the dash panel
• Mounted to the inner fender
• Mounted to a bracket on the engine
The 2 basic types of power steering gears are listed below:
• A recirculating ball system
• A rack and pinion system
In the recirculating ball system, a worm gear converts steering wheel movement to movement of a sector shaft. A pitman arm attached to the bottom of the sector shaft actually moves one tie rod and an intermediate rod move the other tie rod.
In the rack and pinion system, the rack and the pinion are the 2 components that convert steering wheel rotation to lateral movement. The steering shaft is attached to the pinion in the steering gear. The pinion rotates with the steering wheel. Gear teeth on the pinion mesh with the gear teeth on the rack. The rotating pinion moves the rack from side to side. The lateral action of the rack pushes and pulls the tie rods in order to change the direction of the vehicle's front wheels.
The power steering pressure hose connects the power steering pump union fitting to the power steering gear and allows pressurized power steering fluid to flow from the pump to the gear.
The power steering return hose returns fluid from the power steering gear back to the power steering fluid reservoir. The power steering return line may contain an integral fin-type or line-type power steering fluid cooler.
In a typical power steering system, a pump generates hydraulic pressure, causing fluid to flow, via the pressure hose, to the steering gear valve assembly. The steering gear valve assembly regulates the incoming fluid to the right and left chambers in order to assist in right and left turns.
Turning the steering wheel activates the valve assembly, which applies greater fluid pressure and flow to 1 side of the steering gear piston, and lower pressure and flow to the other side of the piston. The pressure assists the movement of the gear piston. Tie rods transfer this force to the front wheels, which turn the vehicle right or left.


Your best bet , take it to a qualified repair shop.

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A lot of times this happens because pressure was held on the steering wheel when the engine was shut off. When the engine is running the power steering pump helps hold the steering wheel in one direction or the other and when you stop the engine that pump pressure stops also so you need to overcome that force while you turn the key. Here's what you do, grab the steering wheel and try to turn it in either direction. It should move freely an inch or so in both directions. If it doesn't then grab it firmly and try to turn it. Left or right. If it feels like it is locked in one direction but turns a little in the other direction then that's the direction you have to rotate it in while at the same time you turn the key on. BTW, what kind of car is it?
Hope this helps.
Dale

This car is essentailly the same as the Lincoln LS & T-Bird.
Here is their solution.

please rate if this helps you. Thanks.

ISSUE: Some 2003-2005 Thunderbird, Aviator, and Lincoln LS vehicles may exhibit steering gear squeak when turning the steering wheel, especially during low speed parking maneuvers. The noise may sound like it is coming from the steering column area and may be felt as a roughness in the steering wheel, while turning.
ACTION: Refer to the following Service Procedure.
SERVICE PROCEDURE NOTE: USE ONLY THE FLUID AND ADDITIVE SPECIFIED IN THIS ARTICLE. USING ANY OTHER FLUIDS OR ADDITIVES MAY RESULT IN SEAL DETERIORATION AND LEAKS.

1. Open the hood and remove the power steering reservoir cap.
2. Raise the vehicle on a hoist. Refer to Workshop Manual, Section 100-00.
3. With engine off, drain power steering fluid by disconnecting steering lines and clamp plate from steering gear. Refer to Steering Gear Removal and Installation procedure in Workshop Manual, Section 211-00, follow only the steps required to disconnect the steering lines.
4. Turn steering wheel lock-to-lock to drain fluid completely.
5. Reconnect steering lines and clamp plate to steering gear. Torque retainer to 15 N-m (11 lb-ft) for Lincoln LS and Thunderbird, torque to 25 N-m (18 lb-ft) for Aviator.
6. Lower vehicle.
7. In a clean container mix 50 ml (10 teaspoons or 1.7 oz.) of Motorcraft Additive Friction Modifier, Part Number XL-3, with 50 ml of Motorcraft MERCON® Multi-Purpose Automatic Transmission Fluid, Part Number XT-2-QDX. NOTE: DO NOT PERFORM STEPS 8 AND 9 ON A HOT VEHICLE.
   
8. Pour the above mixture into the power steering reservoir.
9. Top off (fill) the power steering system with Motorcraft MERCON® Multi-Purpose Automatic Transmission Fluid, Part Number XT-2-QDX and reinstall the power steering reservoir cap.
10. Raise vehicle on hoist enough so the front wheels are off the ground and can be turned from lock-to-lock.
11. Start the engine and keep it at idle. Remain inside of the vehicle.
12. Slowly cycle the steering wheel from lock-to-lock for two (2) minutes.
13. Quickly and forcefully turn the steering wheel in one direction to full lock (either side). Bounce the steering wheel on/off of full lock twenty (20) times forcefully. NOTE: IT IS CRITICAL THAT THE STEERING WHEEL IS TURNED QUICKLY AND FORCEFULLY IN ORDER TO CREATE A PRESSURE SPIKE IN THE POWER STEERING SYSTEM.
    
14. Repeat Step 13 in the other direction. Return the steering wheel to on center position.
15. Slowly turn steering wheel to full lock in one direction (either direction) to achieve maximum pump pressure. Hold at full lock for one (1) second, then turn the steering wheel back 90 degrees as quickly as possible. Repeat this procedure twenty (20) times. NOTE: DO NOT HOLD THE STEERING WHEEL AGAINST THE STOPS FOR MORE THAN THREE TO FIVE (3-5) SECONDS AT A TIME. DAMAGE TO THE POWER STEERING PUMP MAY OCCUR.
    
16. Repeat Step 15 in the other direction.
17. Cycle the steering wheel slowly for 1 minute to confirm that the squeak is corrected and return vehicle to the customer. NOTE: IF THE SQUEAK CONTINUES, REPEAT STEPS 13-16 ONE ADDITIONAL TIME. IF THE SQUEAK IS STILL NOT CORRECTED PROCEED TO STEP 18.
    
18. If the squeak is still present after performing Step 17, replace the steering gear. Refer to Workshop Manual, Section 211-00 for removal and installation procedures.

PART NUMBER PART NAME XL-3 Motorcraft Additive Friction Modifier XT-2-QDX Motorcraft MERCON® Multi-Purpose Automatic Transmission Fluid 5W4Z-3504-A Steering Gear (LS) 5W6Z-3504-A Steering Gear (Thunderbird) 5C5Z-3504-AA Steering Gear (Aviator)

grab the steering wheel and turn it left or to the right and sometimes you might have to put a little effort in it but one way the steering wheel will move about 1-2" and as you are moving it with one hand take the other hand and turn the key and it should turn a lot easier.this is a common thing and if you can try to have the wheels straight and try not to use the steering wheel to get in or out of the vehicle and the wheel should not lock and make it so hard on you.you have to use both hands at the same time one moving the wheel and the other one turning the key but start moving the wheel in the in direction that it moves the most then turn the key.

it may be air in the system tho it should have presented itself before now. if you are unsure of how to bleed the air out of the system, you need only turn the steering wheel all the way one way untill ou hear it making a noise move it completely to the end of it's travel a couple times. repeat that in the other direction. speaking of noise, has the power steering been making any ?

try turning steering wheel a bit, or move shifter up past park. Otherwise ignition may have a broken or stuck pin and will need to be replaced.

If you find you can not unlock your steering column after parking you need to try to pull your steering wheel either to the left or to the right, and it will move an inch or two in one direction or the other. You may have to pull on it with a good effort but do not reef on it or start to bang on it, it will turn a short distance in one direction or the other. After moving it one direction or the other you should then be able to turn the key to unlock the ignition. This happens usually when you park against something while your tires are turned. You turn off the ignition and the power steering pump powers down and releases the pressure to the wheel and puts pressure on your key tumbler or the ignition lock and you can't turn it. It happens on all vehicles. the best way to ensure this does not happen is to have your wheels straight and let go of your steering wheel before you turn off your vehicle.

Lorne