Technical Description
The engine code P0420 indicates that the Catalyst System Efficiency is Below Threshold for Bank 1.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to all makes and models of vehicles (1996-newer). However, the specific repair steps may vary slightly depending on the model. This article applies to Nissan, Toyota, Chevrolet, Ford, Honda, GMC, Subaru, VW, etc.
P0420 is a commonly seen trouble code. Other popular codes include P0171, P0300, P0455, P0442, etc. Be sure to bookmark this site for future reference!
The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate, while the downstream O2 sensor reading should be steady. The P0420 code is triggered if the readings of the two sensors are similar. Oxygen sensors are also known as O2 sensors.
In simplified terms, a P0420 code indicates that the catalytic converter is not working as efficiently as it should be according to specifications. Catalytic converters are not designed to wear out and need replacement, so if they have failed, it is likely due to another underlying issue.
Symptoms
The main symptom for the driver is the illumination of the MIL (malfunction indicator lamp). There may not be noticeable drivability problems, although reduced power output from the vehicle may be felt if the substance inside the catalytic converter is broken or failed, resulting in restricted exhaust.
Causes
A code P0420 may indicate one or more of the following:
Possible Solutions
Some suggested steps for troubleshooting and fixing a P0420 error code include:
Diagnostic Tip
Generally speaking, you can use an infrared temperature gun to measure the temperature of the exhaust just before and just after the converter. The output should be about 100 degrees Fahrenheit hotter when the engine is fully warmed up.
Overall, the biggest mistake vehicle owners make when they have a P0420 code is simply replacing an oxygen sensor (02 sensor) without proper diagnosis. It is important to avoid wasting money by replacing parts unnecessarily.
We strongly recommend replacing the catalytic converter with an original manufacturer brand unit or a high-quality replacement part such as a 50-state legal cat. Cheaper aftermarket catalytic converters may result in the code returning shortly after replacement.
It is worth checking if your vehicle’s emissions-related parts are still under warranty, as many manufacturers offer a longer warranty on these items, even if the bumper-to-bumper warranty has expired.
See also: P0420.com – P0420 Help
