P0420 – Meaning, Causes, Symptoms, & Fixes
Code P0420 Definition
Catalyst system efficiency below threshold (Bank 1).
What Does P0420 Mean?
The function of the catalytic converter is to break down harmful pollutants that are created during the combustion cycle and convert them into harmless gases. Code P0420 indicates that the catalytic converter is not functioning efficiently, therefore increasing the output of harmful pollutants by the vehicle.
- Check Engine Light is on
- Lack of power from the engine
- Decreased fuel economy
- Rotten egg or sulfur smell
- Faulty oxygen sensor
- Worn and internally failing catalytic converter
- Leak in exhaust system
Code P0420 Severity – Moderate
While P0420 does not pose a danger to the driver and may not produce any symptoms with issues related to drivability, it can cause severe damage to other components if not addressed in a timely manner. It is recommended that you address P0420 as soon as possible to keep the cost of the repair to a minimum.
Code P0420 Common Diagnosis Mistakes
Do not overlook other codes that are paired along with P0420. Codes P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0174, and P0171 can give false data readings that create conditions which trigger code P0420. If any other codes are present, they should be addressed first.
Tools Needed to Diagnose:
- Scan your vehicle to verify P0420 is the only code present. If other codes are present, they must be addressed first.
- Examine the exhaust system for damage and leaks. Pay close attention to the exhaust manifold, gaskets, and exhaust pipes pre-catalytic converter. If any leaks are found, repair the leak, clear the code, and complete several drive cycles to verify that was the fix.
- With the car running and at normal operating temperature, use the digital multimeter to check the voltage reading of the downstream O2 sensor. The downstream O2 sensor produces a relatively steady voltage reading of approximately 0.45V if the catalytic converter is functioning properly. If the voltage of the downstream O2 sensor is constantly jumping between 0.1V and 0.9V, the catalyst is worn and the catalytic converter needs to be replaced.