P0420 Diagnosis

P0420 Diagnosis

P0420 Diagnosis

 

The P0420 is commonly refered to as the Cat Code, because replacement of the Catalytic Converter is usually the repair assosiated with this Code. However a few other things must be checked also.

 

This is a picture of a common Catalytic Converter.

 

 

 

This is a picture of a Manifold Converter, notice how it is built into the Exhaust Manifold as a unit. These are obviously more expensive than a normal Converter, require more labor to put in and are commonly found on newer inport Vehicles. Many cars are going in this direction.

 

Im not the type of person who likes to guess at things, i like to have the proper testing equipment to verify what is going on. However i understand that not everyone is going to have these tools. So if you are looking for the most likely option to get rid of this pesky P0420 code, i would first try to verify there is no holes in the Exhaust around the Catalytic Converters / 02 Sensors. If none exist i would replace the Catalytic Converter. Read on for more technical details on this issue including how to see a failed converter on a scan tool.

 

Below is a rather large hole in the Exhaust Pipe

 

 

 

 

If you have a scan tool view the O2 Sensors Data and watch the signals of the Front 02 Sensor and the Rear 02 Sensor for the effected Cat. You should notice that the Front 02 sensor will vary from Lean to Rich. Lean meaning an Air/Fuel Mixture of Mostly Air and Rich meaning a mixture of mostly Fuel.  Fully Lean is represented by a Voltage of 0.1V and fully Rich is 0.9V. Your front 02 Sensor signal should switch back and forth between Lean and Rich rapidly, the rear 02 Sensor when healthy should maintain a steady voltage around .7 Volts or so commonly.

 

Something else you want to check for is an exhaust leak before the Rear 02 Sensor. If extra air is entering the exhaust it will bring that Rear 02 Signal down below .45 when it should be hovering above this number usually. The P0420 Code gets triggered when the computer notices the Rear 02 Sensor Signal starts to look like the Front 02 Sensor. This indicates the Converter has lost its ability to store oxygen and cannot properly treat the Exhaust Gases coming through its Catalyst.