Air Bag warning light code 15

[Les]

I am repairing a 93 celica GT 2.2 for my daughter, I have everything working ecept the air bag light, that was on when we bought the car. I tried the air bag tool that I found posted but it would not stay reset, I seem to be getting a code 15, but can't find a code chart for the air bags, so I do not know what it means. The previos owner had had it to the dealer and he said they dignoised it as the center air bag sensor, since I have been working on it I have replaced the center air bag controler, the clock spring, left and right sensor. and checked all of the fuses. HELP! I would feel much better with my daughter driving this car if I could get this light to go out.
Les