Larger version of 556UW; Designed to handle larger keys which don’t fit the 556UW; For use when installing remote-start products in vehicles equipped with a transponder or RF-based immobilizer system; Immobilizer enables ignition &/or fuel system; If an attempt is made to start vehicle & the transceiver does not receive a valid code, ignition & sometimes fuel systems are disabled; 556UXL bypasses immobilizer system only while the remote start is in use, maintaining the factory system’s integrity; Requires use of a spare key for the vehicle;