Car instantly lost power steering while driving and P/S light came on!

Your power steering is electrically driven. Lexus has a serious problem with the PS failing. To date, February 2016, the complaints have been resolved by the dealerships replacing the steering rack. They are simply hiding the problem, rather than fixing it, since the replacement unit has the same problem as the original. The real problem is a defective electrical connector on the steering rack. That connector does not have a snug fit due to the pins being too small. I fixed mine by snugging the connection with small strands of copper wire inserted into the female part of the connector. You can contact me at nooch@earthlink.net or call me at 805 448 7351 for further guidance. Lee

One fan belt drives the alternator/water pump/power steering pump, if the fan belt broke you could loose the power assist steering and water pump drive (engine would over heat if driven for a few minutes) ant the alternator would not charge the battery. If so start the engine does the battery light stay on? If so turn off the engine open the hood inspect the front of the engine to see if the fan belt encompasses all the pulleys at the front of the engine.