O2 Sensor Contamination
WARNING: This page does not describe the selected car, but rather 20 other vehicles, including the 1994 GMC Yukon, 1994 GMC Vandura Special, 1994 GMC Vandura, 1994 GMC Suburban, and 1994 GMC Rally Camper Special. However, it is still accessible from the selected car via links, so may be relevant.
O2 sensor contamination, caused by silicone in certain fuels or use of improper RTV sealant, may cause a White-powdery coating to cover O2 sensor. The false high signal voltage produced (or low oxygen content sensed) is interpreted by ECM as a rich mixture, causing ECM to set Code 45.