A vehicle’s catalytic converter changes carbon monoxide, hydrocarbons and nitrous oxide into less harmful pollutants. All new cars in Europe have had to have them fitted since 1993, while they’ve been fitted to cars in the US since 1975. Almost every developed country requires every car to have one.
The catalytic converter is part of a car’s exhaust system. Most cars have underfloor cats, which sit roughly beneath the front seats, on the underside of the car. But some have manifold cats, which connect to the exhaust manifold, and others have maniverters, which form part of the manifold.
All catalytic converters work in the same basic way. They have a core or matrix that is coated with rhodium, platinum and palladium.
These metals heat up as the hot exhaust gases pass over them, and the harmful pollutants are turned into carbon dioxide, nitrogen and water.
Catalytic converter problems include impact damage (the matrix can be destroyed if the underside of the car hits an object), a faulty lambda sensor, poor fitting, unburnt fuel in the exhaust (which increases the temperature beyond tolerable levels and causes it to melt) and water damage - the rapid cooling of the matrix (after driving through a ford, for example) can cause the honeycomb matric to break apart.
A catalytic converter works with the lamba sensor and the auto’s ECU. The sensor tells the car’s computer how much oxygen is in the exhaust gases and the engine management system alters the air-fuel mix accordingly. If the sensor or ECU are faulty, the wrong mix can result in damage to the cat.
How long does a catalytic converter last? You should expect a cat to last at least 10 years but most last the life of the vehicle - as long as it isn’t affected by any of the external influences mentioned above.
It isn't illegal to remove a catalytic converter in the UK, but the car is unlikely to pass its annual road-worthiness (MoT) test if it's been removed.