I have a 91 Chevy express that went into antitheft mode how do I get it out

 

Hi, I believe you have a Chevrolet G Van, 1964-1995, not an Express. Sorry, I don't know about the anti-theft mode.

Chevrolet/GMC van Overview Manufacturer Chevrolet/GMC (General Motors) Production 1964–1995 Body and chassis Body style Van Chronology Predecessor Chevrolet Greenbrier Sportswagon Successor Chevrolet Express / GMC Savana