they aren't mandatory they just help keep back pressure in the engine i know that because my friends cut his muffler and catalytic converter off and put pipes so it doesn't have enough back pressure on the engine so it chokes the engine and it vapor locks
THIS IS A RESPONSE TO THE PREVIOUS ANSWER:
I am not sure when the became mandatory but they are in fact are. I believe it started in 1975. They are required to help with pollution. The newer one have an added feature that helps lower oxides of nitrogen which is a key factor in smog. the older ones help convert unburned hydrocarbons (gasoline), and carbon monoxide(
a poisonous gas). These are required by federal emissions laws and you can get in serious trouble if you are caught removing them and driving said vehicle on public roads. So the previous responder was very very wrong by saying that they aren't mandatory
1975
The first year for Catalytic converters was 1975They were first required on all cars in 1975.
1975 and later.
in 1975
1975
They where required for the 1975 model year.
1975
Any vehicle sold in the U.S. since 1975.
In the USA original equipment catalytic converters are generally covered under the 8 year, 80,000 mile federal emissions warranty.
1-3 it depands on the year
The Jeep CJ7 began incorporating catalytic converters in 1975, as part of new emissions regulations implemented in the United States. This change was aimed at reducing harmful exhaust emissions from vehicles. The CJ7 continued to use catalytic converters throughout its production run until 1986.
Tht would vry between countries, but in UK it was 1992.