SON WAS DRIVING VEHICLE & WAS TURNING ROUND A CURB WHEN VEHICLE FAILED TO RESPOND TO STEERING. STEERING WHEEL LOCKED UP, LOST CONTROL OF VEHICLE & HIT A FENCE. HAD APPLIED BRAKES WHICH STOPPED VEHICLE SUDDENLY. DRIVER HIT HEAD ON WINDSHIELD DUE TO AIR BAG NOT DEPLOYING. WAS ABLE TO BACK VEHICLE UP & STEERING WORKED OKAY. HAD EMERGENCY ROOM TREATMENT & RELEASED. *AK