What Does P0420 Mean on a 2020 Nissan Pathfinder?
A P0420 trouble code on your 2020 Nissan Pathfinder means the ECM has detected reduced efficiency in the Bank 1 catalytic converter. The 2020 Pathfinder is the last refresh of the R52 generation, powered by a 3.5L V6 VQ35DD engine producing 284 hp paired with a CVT. Bank 1 is the rear bank (firewall side) on the transversely mounted V6. The Pathfinder uses two close-coupled converters, one per bank, integrated near the exhaust manifolds.
The 3.5L V6 in the Pathfinder is a proven engine, but the converter can wear over time, especially if the vehicle has been used for towing or heavy family hauling.
Symptoms You Might Notice
- Check engine light on
- Reduced fuel economy on an already thirsty SUV
- Sulfur or rotten egg smell from exhaust
- Possible reduced power when towing or climbing hills
- Emissions test failure
Common Causes on the 2020 Pathfinder
1. Deteriorating Catalytic Converter
The Pathfinder's 3.5L V6 generates substantial exhaust volume through each bank's converter. Frequent towing, highway driving, and passenger loading push exhaust temperatures higher, accelerating catalyst wear. The rear bank converter (Bank 1) on the VQ35DD can be slightly more prone to issues due to heat soak from the firewall proximity.
2. Faulty Downstream O2 Sensor
The Bank 1 downstream sensor sits in a high-heat environment behind the rear converter. Heat cycling and contamination degrade sensor accuracy over time. A slow-responding sensor mimics converter failure and should be tested before condemning the converter.
3. Exhaust Manifold Leak
The VQ35DD engine's exhaust manifolds can develop gasket leaks, particularly at the rear bank where access is limited and heat is most intense. A leak here introduces unmetered air before the converter, throwing off downstream O2 sensor readings.
4. Engine Misfire
Misfires send unburned fuel into the converter, causing extreme temperatures that melt the substrate. Ignition coils on the rear bank of the VQ35DD are harder to access and sometimes neglected during maintenance, making them more likely to fail.
How to Diagnose the Problem
- Scan for related codes — Check for misfire codes on specific cylinders, O2 sensor codes, and fuel system codes.
- Monitor O2 sensor data — Compare Bank 1 upstream and downstream readings. A good converter produces a steady downstream signal.
- Check the rear exhaust manifold — Look for exhaust staining or listen for ticking sounds on cold start.
- Temperature test both converters — Compare Bank 1 and Bank 2 converter temperature differentials. If Bank 1 shows less heat rise, its converter is failing.
- Inspect for physical damage — Road debris can dent the converter housing on SUVs that see light off-road use.
Repair Options
Professional Repair
The rear bank converter on the Pathfinder is difficult to access, making professional repair advisable. Diagnosis runs $100-$150. The V6 converter replacement requires removing exhaust components in a tight space. OEM converters for the 3.5L V6 are moderately priced compared to larger truck engines.
DIY Repair
O2 sensor replacement on the rear bank is challenging due to limited access. The converter replacement is a professional-level job on the Pathfinder. If you must DIY, expect to need a lift, proper exhaust gaskets, and 4-6 hours of labor time.
Estimated Repair Costs
- Catalytic converter replacement: $700 - $1,600
- Downstream O2 sensor: $125 - $300
- Exhaust manifold gasket repair: $250 - $600
- Ignition coil/spark plug replacement: $150 - $450
Prevention Tips
- Keep up with spark plug and ignition coil maintenance
- Use quality fuel to reduce converter contamination
- If towing regularly, consider more frequent exhaust system inspections
- Address misfires and rough running conditions immediately
- Monitor fuel economy — a sudden drop may indicate a developing converter problem