The catalytic converters in your Lexus LS400 are three-way converters that lower exhaust emissions through a chemical reaction between the exhaust gas and the substrate in the converter. This type of converter features the reduction capabilities of a reduction converter to lower oxides of nitrogen (NOx) and the oxidation capabilities of an oxidation converter to lower carbon monoxide (CO), carbon dioxide (CO2) and unburned hydrocarbons. Replacement catalytic converters in the Lexus LS400 come installed in an exhaust pipe assembly making replacement easier.
Apply the parking brake and set wheel chocks behind the rear wheels. Raise and support the front of the Lexus using a floor jack and jack stands positioned under the front sub-frame. Lower the car onto the stands slowly so that the weight of the car is supported evenly by the jack stands. Remove the floor jack.
Allow the exhaust system to cool completely. The catalytic converters on the LS400 operate at a high temperature (over 600 degrees Fahrenheit) and can cause severe burns if not allowed to cool sufficiently prior to working on the system.
Spray the attaching bolts on the converter with a liberal coating of penetrating oil and allow it to sit for a few minutes. Remove the two rear mounting bolts that attach each of the converters to the exhaust system using a 13mm socket and ratchet to turn the bolt while holding the 15mm nut with a wrench. Pry the exhaust system back away from the converter and pull the exhaust downward.
Remove the three 13mm nuts that attach the converter to the exhaust manifold and pull the converter off the manifold studs. Use a new exhaust gasket between the converter and manifold. Bolt in the new converter, leaving the nuts loose so the converter can be moved slightly while lining up the rest of the exhaust system.
Raise the exhaust system and pry it back until it can be slipped onto the converter. Place a new gasket between the converters and the exhaust system. Install and tighten all of the nuts and bolts securely.
