P0420 -What Does It Mean? (1997-2001 2.0L Honda CR-V)

When the catalytic converter, on your 2.0L Honda CR-V fails, the fuel injection computer will set a trouble code P0420: Catalyst System Efficiency Below Threshold.

In this article, I'll cover the most common causes of catalytic converter failure and what you should do before replacing it (to avoid a repeat of the problem).

You can find this tutorial in Spanish here: Código P0420 ¿Qué Significa? (1997-2001 2.0L Honda CR-V) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 2.0L Honda CR-V: 1997, 1998, 1999, 2000, 2001.

What Does The Catalytic Converter Do?

To explain the purpose of the catalytic converter it's important to note that the 2.0L engine, in your Honda CR-V, creates and emits harmful pollutants as it runs.

The core pollutants in the engine's exhaust are: hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx).

Hydrocarbons (raw gasoline) are the result of the fuel that doesn't get completely burned in the combustion process.

The catalytic converter is tasked with reducing these harmful pollutants and converting them into harmless gases.

Code P0420 indicates that the catalytic converter is not functioning efficiently and thus not reducing the harmful pollutants your Honda's engine is emitting.

Common Symptoms Of A P0420 Trouble Code

You're gonna' see one or more of the following symptoms:

• The check engine light is on.
• If catalytic converter has broken into pieces, you'll notice a lack of power when you accelerate the engine under load.
• Bad gas mileage.
• Rotten egg or sulfur smell coming out of the tailpipe when the engine is running (especially when you accelerate the engine under load).

What Causes A P0420 Trouble Code?

The P0420 trouble code, lighting up the check engine light on your 2.0L Honda CR-V, is caused by a failing or failed catalytic converter.

A very common misconception is that a bad oxygen sensor will cause a P0420 trouble code. This is simply not true, although it could have contributed to the catalytic converter's demise.

From personal experience I can tell you that number one cause of the bad catalytic converters I've had to replace has been too much raw fuel (hydrocarbons) entering the exhaust and overloading/overheating the catalytic converter.

In troubleshooting a P0420 trouble code, it's important that you check if one of the following issues is present:

1. An excessively rich air/fuel mixture. This condition will overload, overheat, and eventually destroy the catalytic converter's ability to reduce harmful emissions. This excessively rich condition is usually caused by one of the following:
   • Ignition system misfire.
   • Leaking fuel injector(s).
   • Leaking fuel pressure regulator.
   • EVAP canister leaking fuel into the intake manifold.
2. Antifreeze entering the exhaust. This is usually caused by one of the following:
   • Blown head gasket.
3. The engine is burning engine oil.
   • Engine oil, burning inside the cylinder from worn out piston rings, will coat the reactive surfaces of the catalytic converter, reducing its performance.
   • Engine oil, burning inside the cylinder from leaking valve stem seals, coating the reactive surfaces of the catalytic converter, reducing its performance.
   • Adding engine oil anti-wear additives that contain zinc.

Before You Replace The Catalytic Converter

It's important to first troubleshoot and resolve any problems that can cause the catalytic converter to fail.

If you don't, then the new catalytic converter will eventually lose its ability to reduce harmful emissions and fail. You'll again see the check engine light illuminated by a P0420 trouble code.

I recommend that you troubleshoot and resolve any problem that could be:

• Overloading the exhaust with hydrocarbons (raw gasoline).
• Causing anti-freeze to enter the exhaust gas.
• Causing engine oil to enter and burn in the engine cylinders.

In my experience, the most common cause of a bad catalytic converter has been a misfire problem. So if you have a misfire trouble code stored in the fuel injection computer's memory (P0300, P0301, P0302, P0303, P0304), solve them first.

If any other trouble codes are present along with the P0420 trouble code, troubleshoot and resolve them first before replacing the catalytic converter.

More 2.0L Honda CR-V Tutorials

You can find a complete list of tutorials here: Honda 2.0L Index Of Articles.

Here's a sample of the tutorials you'll find there:

• How To Test For A Blown Head Gasket (1997-2001 2.0L Honda CR-V).
• How To Test The Ignition Coil (1999-2001 2.0L Honda CR-V).
• How To Test The TPS (1997-2001 2.0L Honda CR-V).
• How To Test The MAP Sensor (1997-2001 2.0L Honda CR-V).
• How To Test Engine Compression (1997-2001 2.0L Honda).