Code P0420 on your 2020 Dodge Durango indicates the catalytic converter on bank 1 isn't cleaning exhaust gases as efficiently as it should. But before replacing an expensive converter, it's worth understanding what can trigger this code—because sometimes the converter isn't the real problem.
Understanding P0420
The PCM monitors catalytic converter efficiency by comparing the upstream and downstream oxygen sensor readings. A healthy converter causes the downstream sensor to show a relatively steady signal while the upstream sensor fluctuates. When the downstream sensor begins mimicking the upstream sensor's fluctuations, the PCM determines converter efficiency has dropped and sets P0420.
What Bank 1 Means
On the Durango's V6 or V8, bank 1 is typically the side with cylinder 1—the driver's side on Pentastar V6 and passenger side on Hemi V8. Check your specific engine configuration to ensure you're addressing the correct converter if there are two.
Common Causes
Actual Converter Degradation
Converters do wear out. The catalyst material breaks down over time, especially with high-mileage vehicles or exposure to contaminants like oil, coolant, or poor fuel. This is the code's intended detection purpose.
Oxygen Sensor Problems
A lazy or failing downstream O2 sensor can provide data that looks like converter inefficiency even when the converter is fine. Sensors degrade faster than converters and are much cheaper to replace.
Exhaust Leaks
Leaks between the engine and downstream sensor introduce atmospheric oxygen into the exhaust stream, confusing the sensor readings. The system reads this as converter inefficiency.
Engine Running Rich or Lean
Long-term fuel mixture problems stress the converter. Running rich can overheat and melt the catalyst; running lean causes elevated temperatures and premature breakdown.
Oil or Coolant Contamination
Engine problems allowing oil or coolant into the exhaust coat the catalyst material, reducing efficiency. This points to additional engine problems needing attention.
Diagnostic Steps
- Check for other codes: Misfire codes, fuel trim codes, or O2 sensor codes indicate underlying problems causing converter stress.
- Inspect O2 sensors: Compare upstream and downstream sensor readings. Test sensor response time.
- Check for exhaust leaks: Listen and look for leaks between engine and downstream sensor.
- Monitor fuel trims: Long-term fuel trims outside ±10% indicate mixture problems that can damage converters.
- Physical converter inspection: Inspect for physical damage, rattling (broken substrate), or external contamination.
Repair Options
O2 Sensor Replacement
If the downstream sensor is sluggish or failed, replacement may resolve the code. Cost: $150-$300.
Exhaust Leak Repair
Fix any leaks upstream of the downstream sensor. Cost: $100-$400 depending on leak location.
Address Underlying Engine Problems
If mixture issues or oil consumption are killing converters, fix the root cause before replacing the converter.
Catalytic Converter Replacement
If the converter is genuinely failed, replacement is necessary. OEM converters meet specifications but are expensive. Aftermarket options exist but quality varies. Cost: $800-$2,500 depending on type.
Can You Drive With P0420?
The vehicle remains drivable—P0420 doesn't indicate an immediately dangerous condition. However, you'll fail emissions testing, and ignoring converter problems can mask issues that worsen over time.