One of the most common codes we pull up is the “P0420” code. This is usually followed by something like “Catalyst Efficiency Below Threshold (Bank 1). There are many problems that can cause this code, including the need to replace the Catalytic Converter. This can be quit costly and is not a very welcomed diagnosis. We have found that a good place to start is the replacement of the Oxygen Sensor downstream from the catalytic converter. However be aware, no matter how many times we warn that this is not the cure all for the code; there are times that the converter just needs to be replaced. What we try to tell customers is that this is just a good place to start, a $100-$200 Oxygen sensor ( installed) is certainly better then a $600-$1200 converter. When they are given the option customers are usually willing to take the chance ( many times this is successful) however many times they forget that we were trying to guide them from replacing the more expensive converter. In reality the Oxygen sensor is certainly not a waste of money. Many times changing out the sensor is just something that would need to be done in the future. Listen to your mechanic closely. Some vehicles seem to have common problems that the mechanic will recognize and be able to give his/her opinion as to where to start on the repairs.

Common causes for Engine Code “P0420”

Three way catalyst converter Bank 1

Exhaust tube Intake air leaks

Fuel injectors may be faulty

Fuel injector leaks

Spark plugs may be faulty

Improper ignition timing

Engine Control Module (ECM)

Downstream Oxygen Sensor

Upstream Oxygen Sensor

Catalytic Converter