Code 55, ECM/Pcm Error (Except 2.5L)
WARNING: This page does not describe the selected car, but rather 24 other vehicles, including the 1992 GMC Yukon, 1992 GMC Vandura Special, 1992 GMC Vandura, 1992 GMC Value Van, and 1992 GMC Suburban. 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.