Possible Causes
WARNING: This page is about a different car, the 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.
DTC 15/B1156 or B1157 could be causes by an open or short circuit between front air bag sensor and air bag sensor assembly, short to battery in front air bag sensor circuit, or front air bag sensor malfunction.