The 2018 Acura RDX's steady check engine light with P0420 indicating catalyst system efficiency below threshold requires careful diagnosis before assuming the catalytic converter has failed. Understanding what triggers this code helps avoid unnecessary replacement of expensive emissions components.
Understanding P0420 in the RDX V6
P0420 sets when the ECU detects reduced oxygen storage capacity in the Bank 1 catalytic converter. The system compares upstream and downstream oxygen sensor waveforms. A healthy catalyst shows distinctly different patterns—similar waveforms indicate the catalyst can no longer effectively buffer oxygen fluctuations during combustion.
Causes Beyond Converter Failure
Faulty oxygen sensors can trigger P0420 by providing incorrect readings. Exhaust leaks before the downstream sensor affect oxygen measurements. Engine misfires damage catalysts with unburned fuel. Rich or lean running stresses the catalyst over time. Recent extensive idling may affect the ECU's catalyst efficiency testing.
Diagnostic Priorities
Check for additional codes indicating engine problems that affect catalyst health. Test both oxygen sensors for proper operation and response time. Inspect for exhaust leaks between the engine and downstream sensor. Review fuel trim data for evidence of mixture problems. Evaluate catalyst efficiency through sensor waveform comparison.
Repair Considerations
Address any underlying engine issues before converter replacement. If sensors are faulty, replacement costs far less than a new catalyst. For confirmed converter failure, OEM replacements ensure proper fit and compatibility. Aftermarket converters may be acceptable but must meet EPA or CARB requirements.