Code 51, Faulty Prom/Mem-Cal
WARNING: This page is about a different car, the 1994 Chevrolet Caprice and 1994 Buick Roadmaster. However, it is still accessible from the selected car via links, so may be relevant.
Ensure all pins are fully inserted in socket. If pins are okay, replace PROM/MEM-CAL, clear memory and recheck. If Code 51 reappears, replace control module.