Catalysts often last 10 years, but actual life depends on mileage and engine tune. 50,000 miles is a more reasonable benchmark, and you can generally expect to replace the catalytic converter once during the life of a vehicle.
If failure occurs early, it's important to find and fix the cause of the problem before fitting a new CAT otherwise the replacement can be expected to fail prematurely too.
There are three main ways they fail:
- Melt down - unburned fuel enters the catalyst and ignites on contact. The extreme heat literally melts the ceramic matrix. Poor ignition timing, a faulty oxygen sensor, worn or defective spark plugs, incorrect fuel mixture and other ignition/fuel injection related faults could lead to this failure.
- Carbon deposits - oil or antifreeze entering the combustion chamber/exhaust system can lead to a build up of carbon on the matrix, which increases back pressure leading to overheating and poor performance.
- Catalyst fracture - the ceramic matrix is fragile and can break-up as a result of excessive vibration or external impact. As the matrix breaks up back-pressure increases and overheating can result.