Code 55, ECM/Pcm Error
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1994 GMC Vandura, 1994 GMC Rally, 1994 GMC Pickup, 1994 Chevrolet Sportvan, and 1994 Chevrolet Pickup. However, it is still accessible from the selected car via links, so may be relevant.
Ensure ECM grounds are good and MEM-CAL is properly latched. If okay, replace ECM/PCM. Clear codes and confirm closed loop operation. Check operation of SERVICE ENGINE SOON light.