How To Find Out If The Catalytic Converter Is Bad (1996-2007 2.4L Caravan, Grand Caravan, Voyager, Grand Voyager)

At some point, you're gonna have problems with your minivan's catalytic converter. When that happens, your minivan's OBD II fuel injection computer will light up the check engine light and register a P0420 code.

If you find yourself in this situation, this tutorial will explain what you need to know about trouble code P0420 and also show you how to figure out if the catalytic converter is working as it should or if it needs to be replaced.

APPLIES TO: This tutorial applies to the following vehicles:

• 2.4L Chrysler Voyager: 2000, 2001, 2002, 2003.
• 2.4L Dodge Caravan: 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007.
• 2.4L Dodge Grand Caravan: 1996, 1997.
• 2.4L Plymouth Voyager: 1996, 1997, 1998, 1999, 2000.
• 2.4L Plymouth Grand Voyager: 1996, 1997.

Trouble Code P0420 Basics

Having a P0420 diagnostic trouble code registered in the fuel injection computer's memory means that your Dodge/Plymouth minivan's catalytic converter isn't doing its job. Specifically, it's saying that the converter isn't cleaning out the hydrocarbons —essentially unburned gas— from your minivan's exhaust.

In a nutshell, the catalytic converter's main function is to filter hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). These gases are the byproduct of the combustion process in your minivan's engine. The converter breaks them down into less harmful gases before they exit your minivan's tailpipe.

Without diving into technical details, here's what the converter does:

1. Even when operating correctly, the engine doesn't fully burn all the gasoline it consumes. The combustion process also creates carbon monoxide (CO) and nitrogen oxides (NO_x). Although not ideal, this is normal.
2. The unburned gasoline (HC), CO, and NO_x, from the four cylinders get pushed into the exhaust system and are routed to the catalytic converter.
3. Once inside the catalytic converter, the HC, CO, and NOx gases oxidized and broken down into their basic components:
   • Hydrocarbons (HC) are converted to carbon dioxide and water.
   • Nitrogen oxides (2NO_x) are converted to nitrogen and water.
   • Carbon monoxide (CO) is converted to carbon dioxide.
4. Generally, if a cylinder is misfiring or if a fuel injection system input sensor fails, the computer is programmed to inject more gasoline than necessary. This causes a rich air/fuel mixture that will lead to the catalytic converter overheating, which over time will damage it and trigger a P0420 trouble code to illuminate the check engine light.

I'm sure you've noticed water dripping from your vehicle's exhaust pipe when the engine is running. Well, this water is the result of the oxidation process that the catalytic converter is causing.

NOTE: In my hands-on experience, most of the time a P0420 trouble code is registered in the fuel injection computer's memory, it means the catalytic converter is shot and needs replacing. But I've also seen a few exceptions where something else was the root cause.

Symptoms Of A Bad Catalytic Converter

The signs that you have a malfunctioning catalytic converter —or the lack of any— vary based on the type of failure it has suffered. To be a bit more specific, the catalytic converter typically fails in one of two ways:

1. The internal filtering component of the catalytic converter wears out and stops oxidizing (filtering) the exhaust gases. In this type of failure, the filtering component remains intact (in one piece) and generally doesn't cause an engine performance problem.
2. The filtering component inside the catalytic converter fractures into multiple fragments. In these cases, engine performance is affected.

Depending on how the catalyst fails, you'll notice one or more of the following:

1. The catalyst's filtering element has NOT broken into pieces:
   • The Check Engine Light is on.
   • The P0420 code is present.
   • A 'rotten egg' smell comes out of the exhaust pipe when the engine is running.
   • Fails the state mandated emissions check.
   • Bad gas mileage.
   • The engine appears to be running well. In other words, it's not lacking power, the engine idles smoothly, and it doesn't hesitate when accelerating the vehicle on the road.
2. The catalyst's filtering element HAS broken into pieces:
   • Lack of power. This lack of power is caused by the broken pieces of the filtering element restricting the exhaust gas flow.
   • The vehicle hesitates when accelerating on the road.
   • Rough idle.
   • A rattling noise coming from under the vehicle when the engine is running or when accelerating.
   • The Check Engine Light is on.
   • The P0420 code is stored in the memory of the fuel injection computer.

Let's take a look at the next section and find out why the catalytic converter fails.

What Causes The Catalytic Converter To Fail?

The catalytic converter will eventually fail on its own, but several things can speed up the process:

1. An excessively rich air/fuel mixture that causes the catalytic converter to overheat. This rich air/fuel mixture is generally the result of:
   • A cylinder misfire caused by a lack of spark.
   • A faulty fuel injector that's leaking gasoline.
   • A faulty fuel pressure regulator letting gasoline pass through its vacuum inlet (if equipped with one).
   • An EVAP system issue allowing liquid fuel (instead of vapor) into the intake manifold.
2. Engine antifreeze/coolant burning inside the cylinders and entering the exhaust system. This antifreeze now coats the reactive surface of the catalytic converter's filtering element (reducing its performance). This problem is usually caused by:
   • A blown head gasket.
   • Engine antifreeze/coolant entering the cylinders through a faulty intake manifold gasket.
3. Engine oil burning inside the cylinders and coating the reactive surface of the catalytic converter's filtering element (reducing its performance).
   • Worn piston rings that are letting oil pass and burn in the cylinder.
   • Damaged cylinder head valve seals that are letting oil leak into the cylinders.
   • Adding oil additives that contain the metal zinc.
   A sign that engine oil is burning inside the cylinders is blue smoke coming out of the tail-pipe.

In case you're wondering what a 'rich air/fuel mixture' is. In simple terms, it's when there's too much gasoline in the mix of air and fuel that your engine uses to operate.

This extra gasoline doesn't get burned during the cylinder's combustion process and makes its way into the exhaust system and into the catalytic converter. This overloads the converter, causing it to overheat and eventually fail.

A sure sign that that your minivan's engine is running with a rich air/fuel mixture is black exhaust smoke coming out of the tailpipe.

If you're dealing with any of these issues in your minivan, you'll want to resolve them before replacing the catalytic converter. Otherwise, the new one will fail in no time. Let's turn the page and dive into the tests!