P0420

Catalyst System Efficiency Below Threshold (Bank 1)

What does this mean?  Well it means that the catalytic converter isn't working the way it should, or at least appears that way to the computer.  

The cause is usually a contaminated or blocked cat.  To see a list of what causes cats to die, see the Catalytic Converter page.  In order to fix it properly and not kill your new cat, you would need to find and fix the root cause(s) first.

One way to get rid of the MIL for testing or off-road purposes, is to put a spacer in between the rear o2 sensor and the bung.  This effectively moves the sensor slightly out of the exhaust stream so that it shows less fluctuation, exactly what the computer is looking for.  A trip to your LAPS and ~$6.50 will get you a set of 2 'spark plug anti-fowlers'.  Dorman Help 42009 http://amzn.to/2p4VsdD

Will that affect the performance of my van?  The downstream(rearmost, after-cat, the back one) o2 sensor is only used to make sure the catalytic converter is working, once heated up.  It has zip/zero/zilch/nada affect on engine performance.

Should I remove my catalytic converter?

Only if you want to make the world a worse place and violate the law. While there may be legitimate reasons to remove a catalytic converter, I can only think of 1 possible reason(travel in areas with contaminated fuel) and performance isn't one of them. The newer high performance cats are going to cost you maybe(and that is a big maybe) 1% horsepower, usually at the top end, hardly worth fussing over.

• • It is a violation of Section 203(a)(3)(A) of the 1990 Clean Air Act in the USA for a vehicle repair shop to remove a converter from a vehicle, or cause a converter to be removed from a vehicle, except in order to replace it with another converter.

  • Section 203(a)(3)(B) makes it illegal for any person to sell or to install any part that would bypass, defeat or render inoperative any emission control system, device or design element.

These are what you are looking for, they are in the help section.

The inside diameter won't fit the o2 sensor, so you have to make the hole bigger with a 1/2in drill bit, or equivalent.

You can use a special o2 socket to remove the rear o2 sensor, or if you already have a box end wrench to fit you can just trim the connector a bit so that the box end will slide over it.  Even after trimming the connector still latches closed when connected.