1997 LEXUS SC400

TWO WEEKS AGO A RED WARNING LIGHT APPEARED ON THE DASH SHOWING AN AIR BAG DEFICIENCY. THE CAR WAS TAKEN TO LEXUS OF WAYZATA FOR DIAGNOSTICS AND REMOVAL OF THE WARNING LIGHT. I LATER RECALLED THE BATTERY HAD DRAINED DUE TO A POOR CONNECTION ABOUT THE TIME THE LIGHT CAME ON. THAT WAS FIXED BUT THE LIGHT STAYED ON. LEXUS WANTED OVER $1600 TO OBTAIN A NEW AIR BAG SENSOR MODULE INCLUDING LABOR COSTS, BROKEN DOWN INTO PARTS COST $1150 AND LABOR $470. I FURNISHED THE USED SENSOR ON THE INTERNET FOR $95 AND THE LIGHT DISAPPEARED. SAVED OVER $1000 BY TAKING CHARGE OF REPAIRS. THERE WAS NO ACCIDENT INVOLVING THIS CAR. MY UNDERSTANDING IS FOLLOWING RESEARCH INTO THE PROBLEM THAT CERTAIN SOFTWARE REMOVAL TOOLS COULD HAVE CLEARED THE BATTERY DRAINAGE EVENT. I DO NOT KNOW IF LEXUS ATTEMPTED THIS REPAIR. I HAVE THE ORIGINAL SENSOR IN MY POSSESSION AND WITH THE SOFTWARE TOOL APPLICATION CAN PROBABLY ASCERTAIN IF THIS WAS THE PRECISE PROBLEM.. SHOULDN'T THE DEALERS BE REQUIRED TO INVESTIGATE POTENTIAL REPAIRS BEFORE REPLACEMENT OF SENSORS?