A P0420 diagnostic code on your 2016 Honda Civic indicates the catalytic converter efficiency has fallen below acceptable thresholds. As a first-year 10th-generation Civic, your vehicle may have the 2.0L naturally aspirated or 1.5L turbocharged engine.
Why P0420 Appears
The ECM compares oxygen sensor readings before and after the catalytic converter. When the converter is working properly, the downstream sensor shows a relatively steady voltage. When efficiency drops, downstream readings begin mimicking the upstream sensor's fluctuations, triggering P0420.
Common Causes
- Converter Age: At 8+ years old, natural wear is possible
- Contamination: Oil, coolant, or fuel contamination
- O2 Sensor Issues: Faulty sensors causing false readings
- Exhaust Leaks: Air intrusion affecting measurements
- Past Misfire Damage: Previous engine issues affecting converter
- 1.5T Specific: Oil dilution issues on turbo models