Cadillac 25939989 3Way Catalytic Convertor Assembly

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Raise the front of the vehicle and support it securely on jackstands, then remove the engine under-cover. Locate the upstream and downstream oxygen sensors, trace their electrical leads to their respective connectors, and disconnect them before removing both oxygen sensors. If the catalytic converter or exhaust manifold has a heat shield, remove the heat shield bolts and take off the heat shield from the exhaust manifold. Next, remove the fasteners securing the heat shield mounting bracket and take off the bracket. Remove the fasteners that secure the catalytic converter's upper mounting flange to the exhaust manifold, applying penetrant to the threads if they are severely damaged or rusted, and wait before loosening them. Similarly, remove the fasteners securing the lower mounting flange to the exhaust pipe, using penetrant if necessary. Pull the exhaust pipe down far enough to clear the lower end of the catalytic converter, then remove the catalytic converter from the exhaust manifolds. Finally, remove and discard the old gaskets between the exhaust manifold flange and the upper catalytic converter flange, and if equipped, between the lower catalytic converter flange and the exhaust pipe flange. Installation is the reverse of removal, ensuring to use new flange gaskets.