In order to replace the Catalytic Converter on 4.81- and 5.31- engines the first task to undertake is to raise and support the vehicle. Unbolting then remove the engine shield bolts and shield, and oil pan skid plate bolts and plate if needed. Pull out the Oxygen Sensor connection from the floor reinforcement, remove the clip around the engine harness and air sensor pigtail, and remove the connector position assurance (CPA) retainers and Oxygen Sensor electrical connectors. Disconnect the Oxygen Sensor electrical connectors from the hose clip and transmission crossmember, and remove cpa retainers, and Oxygen Sensor electrical connectors (1, 2). Take off the left and right exhaust manifold pipe nuts, exhaust muffler nuts, and then the Catalytic Converter. In the case of replacing the Catalytic Converter apply anti-seize compound gm p/n 12377953 or equivalent to the threads of the old oxygen sensors; install and tighten to 42 nm (31ft.lbs). Next, then install the catalyticconverter and new exhaust manifold pipe seals to the exhaust manifolds followed by the right and left exhaust manifold pipe nuts, tighten thetop to fifty nm (39 ft.Words). Attach the exhaust muffler nuts and tighten them to 40 nm (30 ft. Lbs.). Connect the Oxygen Sensor electrical connectors (1,2) and the cpa retainers, and attach the oxygen sensors electrical connectors to the hose clip and transmission crossmember. Connect the Oxygen Sensor electrical connectors and the cpa retainers, install the clip through the engine harness and the Oxygen Sensor pigtail and clip the connection of the Oxygen Sensor to the floor reinforcement. Lastly, install the oil pan skid plate and the bolts if needed with a torque of 20 nm (15 ft. Lbs.) followed by the engine shield and bolts if needed with a torque of 20 nm (15 ft. Lbs.); then lower the vehicle.