OBD2 fault code P0420 is a common fault code. This code is generated when the vehicle’s ECU detects a low efficiency of the catalytic converter. This activates the Check Engine light on the dashboard to warn the user that there is a fault in their vehicle, so that they can perform a scan to determine the specific problem.
Why does fault code P0420 occur?
The P0420 obd2 fault code is generated when the readings of the 2 oxygen sensors or lambda probes that the catalytic converter has generate very similar readings, that is, both the inlet sensor and the outlet sensor of the catalytic converter show similar values, this is interpreted by the vehicle’s ECU as an indication that the catalytic converter is not correctly fulfilling its function of controlling polluting emissions.
How to resolve fault code P0420?
There are multiple causes that can generate this code. A good approach is to eliminate the following factors point by point. It’s recommended to work from the simplest and most cost-effective cause to the most expensive. I recommend following this order:
Inspect complete exhaust system
It is important to rule out any exhaust gas leaks from the exhaust manifold to the muffler, including of course the catalytic converter and its connections.
Check the operation of oxygen sensors
It’s necessary to check that the oxygen sensors are working properly with a scanner, checking for any associated fault codes and that graphical tests with a scanner or oscilloscope indicate they are working correctly. If one of the two sensors is defective, it must be replaced.
Catalytic converter inspection
A catalytic converter inspection is crucial. If, after checking the previous two items, the code reappears, you should check that the catalytic converter is not damaged, clogged, or has damaged internal cells. Once exhaust system leaks and malfunctioning oxygen sensors have been ruled out, it can be established by elimination that the catalytic converter is the problem. If it is clogged, it can be unclogged with specific treatments to remove carbon deposits. If the internal cells are physically damaged, the only option is to replace the catalytic converter.
False positives of the Obd2 code P0420
In some circumstances, the P0420 code may be activated during cold starts, that is, in low ambient temperatures. This occurs because the oxygen sensors and the catalytic converter have an ideal working temperature. In order to measure efficiently, the sensors have a heating element, which allows the sensor to reach a certain temperature for a more accurate measurement. Furthermore, the catalytic converter needs a working temperature to internally generate a reduction in polluting gases. When the car is started on a cold morning and immediately driven off, the internal measurement may be inaccurate and generate a false activation of this fault. Therefore, in some cases, when this code is present, the module is usually reset using the equipment or a diagnostic interface via a scanner to see if the fault reappears during a new driving cycle.
