P0420 code shows

SOURCE: '02 civic engine code P0420. What does this mean?

it means your 02 sensor pre cat is not working or the cat is no longer any good start with the 02 sen its easy to do and cheaper than the cat

SOURCE: service engine light comes on code is p0420

catalytic converter below threshold due to engine needing tune up which leads to plugging of cat or replace 02 sensor if heater circuit has malfunction

SOURCE: P0420 code

This means that the secondary O2 sensor detects that the catalytic converter isn't working as efficiently as it should.
This engine code can be triggered by any one of the following:

1.) The catalyst in the catalytic converter is cracked, clogged, or otherwise damaged.
2.) The secondary O2 sensor is malfunctioning.
3.) There is an exhaust leak.
4.) The computer unit is faulty.

SOURCE: 2001 golf gti had fault

re the funny smell, i need to speak to my friend as i have never heard of that one,does it smell of rotten eggs???

SOURCE: Check engine light is on. Code is showing P0420.

This code means the downstrean (behind) O2 sensor determines a reduced level of effectiveness in the cat. converter-it may not be 'lighting off' (600+ degrees) to burn any hydrocarbons left over from the combustion process. I can be that the cat is bad, or there is an exhaust leak before the cat, or the sensor itself is bad. You can do a visual inspection to determine if there is a leak, and use a scanner to see if the O2 sensor is working properly. It should read a fairly steady voltage and not switch nearly as fast as the upstream O2 sensor. The downstream O2 sensors only purpose is to monitor the cat-you might try clearing the Check Engine Light first to see if it comes back. Then you should consider contacting your dealer since you may be covered under an extended warranty that they have to put on emission devices.