P0420: Efficacité du système catalytique inférieure au seuil (Ligne 1)
Efficacité du système catalytique inférieure au seuil (Ligne 1) : Oxygen sensor 2 (downstream) waveform mirrors upstream O2 sensor, indicating reduced oxygen storage capacity in the three-way catalytic converter.
| Trouble Code (DTC) | P0420 |
|---|---|
| Official SAE Definition | Efficacité du système catalytique inférieure au seuil (Ligne 1) |
| Vehicle Subsystem | powertrain |
| Driving Severity | MEDIUM |
Observable Symptoms
- Check Engine Light (MIL) illuminated
- Sulfur or rich exhaust odor
- Failed emissions / OBD readiness test
Most Probable Root Causes
- Aged or thermally degraded three-way catalytic converter
- Exhaust manifold or flex-pipe leak upstream of rear O2 sensor
- Lazy or contaminated downstream oxygen sensor (Bank 1 Sensor 2)
- Engine misfire or fuel trim imbalance poisoning catalyst
Step-by-Step Diagnostic Procedure
- Compare Bank 1 Sensor 1 and Sensor 2 live voltage graphs at 2,000 RPM warm cruise
- Inspect exhaust system for leaks between manifold and rear sensor
- Verify long-term fuel trims (LTFT) are within ±8% and no misfire codes are stored