So your Lexus ES300 had the engine light on, and you used a scanner to figure out the problem. Results showed P0420 and/or P0430: bad catalytic converter/s. But the part isn't supposed to fail by itself. Problems are often a result of issues outside the operating capacity of a converter. A malfunctioning unit is a symptom of deeper and more alarming engine and exhaust problems you should take care of immediately. Simply installing a new catalytic converter would only serve as a temporary repair. Here are a few examples of the common problems experienced by aging units and their underlying causes.
The easiest way to tell if something's wrong with your Lexus ES300 catalytic converter is when you begin to notice a foul, rotten-egg smell. This is a sign of a converter operating too hot. Check the temperature of the converter's inlet and outlet to verify the diagnosis. This is a result of the engine working with too much fuel during combustion. There may also be an ignition misfire, compression leak, leaky valves, and others. The unburned fuel goes to and gets processed inside the catalytic converter to produce the bad smell.
The following are some signs of a Lexus ES300 poorly running: stutters, slow acceleration, jerks, low power, and stalls. You may also notice a drop in fuel efficiency. If these are experienced, you may have a plugged converter caused by excessive backpressure. It's also possible that other parts of the exhaust-headers, mufflers, pipes-are the ones plugged. To be sure that the converter is the one causing problems, remove it from the system and try to pass a beam of light through it. If the light's not visible, then it's plugged. Work on the other components as well to solve the problem.
You may see that the exhaust fumes coming out of the tailpipe is colored black or blue. Just like liquid fuel in the converter, this is caused by an engine that's already burning engine oil during combustion. There are leaks that allow the oil to enter the combustion chamber. This new mixture results to a new kind of exhaust fume that is not designed to pass through the converter. To combat this, not only should the converter be worked on, but valves and rings in the engine should be replaced as well.