OBD II trouble code P0420 Catalyst Efficiency Below Threshold (Bank 1) is one of the most common codes encountered on the GM 3.8L equipped cars and mini-vans.
In the majority of the cases, this code points to a bad catalytic converter. In this tutorial, I'm gonna' show you some of the basics you need to know about what DTC P0420 means and a step-by-step test on how to test it.
Here are the contents of this tutorial at a glance:
One of the most important things we need to know is that code P0420 is referring to the performance of the catalytic converter on your 3.8L V-6 equipped GM car or mini-van. Specifically, that the catalytic converter is not cleaning up the exhaust of hydrocarbons like it should.
In case you're wondering what the heck are hydrocarbons?... in a nutshell, and as it applies to automobiles, this word refers to gasoline... specifically the unburned gasoline that flows into the exhaust after the combustion process.
As you're probably already aware, the catalytic converter is tasked with cleaning as much of the hydrocarbons, that don't get burned in the cylinder during the combustion process, as it can. Although I'm not going into minute technical detail, on how the cat works, here are some more specifics about what it does:
If you've ever noticed water dripping out of the exhaust of a running car... then you're seeing the end result of the oxidation process happening inside the catalytic converter.
The symptoms (or lack of symptoms) of a BAD catalytic converter depend on the way the catalytic converter has failed. I'll explain...
...There are two specific ways the catalytic converter fails. One is where the honeycomb filter element inside the catalytic converter simply wears out and can no longer clean the exhaust but, remains intact (in one piece). The other is when the honeycomb filter element shatters into several pieces.
Depending on how the catalytic converter fails... you'll see the following:
Let's take a look at the next subheading and find out why the catalytic converter fails.
The catalytic converter will eventually fail all on its own... but what accelerates its demise are several things:
What's a Rich condition? This is when the engine is consuming an excessive amount of fuel. This excessive amount of fuel, entering the engine, causes raw fuel (hydrocarbons) to pass into the exhaust and into the catalytic converter. Once in the catalytic converter, this excessive amount of fuel causes the catalytic converter to overheat and fail.
Knowing that your vehicle has any one of the above conditions/problems, will help you to make an informed decision as to what needs to get repaired to successfully solve the P0420 Catalyst Efficiency Below Threshold (Bank 1) trouble code.
Alright, let's turn the page and get testing!.....
“This planet has - or rather had - a problem, which was this: most of the people living
on it were unhappy for pretty much of the time. Many solutions were
suggested for this problem, but most of these were largely concerned
with the movement of small green pieces of paper, which was odd
because on the whole it wasn't the small green
pieces of paper that were unhappy!”
The Hitchhiker's Guide to the Galaxy