I have a 2005 Allure, 3800 engine, floor shift automatic, power steering uses engine driven hydraulic pump. Fluid in pump is normal, no noise comes from pump, no check engine or service warning lights lit on instrument cluster. This car does not have a mechanical steering wheel lock as some older one did. The steering wheel rotates freely lock to lock with engine on (power assisted) and with engine off.

On three occasions the following has happened-
1. I have parked in a parking lot. No problems/noise. Steering wheel/ tires are centred.
2. Upon returning to the car, it has started with no noise other than motor running.
3. When backing up (twice) or going forward (once), the steering wheel has locked
solid. It will not turn right or left. I can hang on it and still it refuses to move.
4. I turn off the car and then immediately restart. Steering works normally. Moves as
it should from left to right and back again.

This week, I removed- air bag, steering wheel, clock spring, turn signal control, ignition switch. I was down to the joint that allows for tilt steering. I could not find any mechanical reason for lockup of steering wheel. There is no noise or play in the lower intermediate steering shaft.

Any help would be greatly appreciated.