DTC B1815/54 Short in Front Passenger Side Squib 2nd Step Circuit; DTC B1816/54 Open in Front Passenger Side Squib 2nd Step Circuit; DTC B1817/54 Short to GND in Front Passenger Side Squib 2nd Step Circuit; DTC B1818/54 Short to B+ in Front Passenger Side Squib 2nd Step Circuit: Wiring Diagram
WARNING: This page is about a different car, the 2008 Lexus IS F. However, it is still accessible from the selected car via links, so may be relevant.