What Does P0420 Mean on a 2020 Nissan Murano?
A P0420 code on your 2020 Nissan Murano means the ECM has determined that the Bank 1 catalytic converter is not efficiently processing exhaust gases. The 2020 Murano rides on the D-platform and is powered by the 3.5L V6 VQ35DE engine producing 260 hp, paired with Nissan's Xtronic CVT. Bank 1 is the rear cylinder bank on the transversely mounted engine. The Murano uses close-coupled catalytic converters integrated near the exhaust manifolds.
The VQ35DE in the Murano is a well-proven engine, and P0420 is typically caused by normal converter aging or a sensor issue on vehicles with several years of driving.
Symptoms You Might Notice
- Check engine light on
- Mild decrease in fuel economy
- Sulfur or rotten egg odor from exhaust
- Slight hesitation during acceleration
- Emissions test failure
Common Causes on the 2020 Murano
1. Catalytic Converter Wear
The Murano's 3.5L V6 produces moderate exhaust volume through each bank. City driving and frequent short trips create thermal cycling that degrades the converter. The close-coupled design means the converter sits in a high-temperature zone near the engine, which accelerates the aging process.
2. Faulty Downstream O2 Sensor
The Bank 1 post-cat sensor monitors exhaust composition after the converter. Heat and contamination gradually reduce sensor accuracy. A slow-responding sensor is one of the most common and affordable fixes for P0420 on the Murano.
3. Exhaust Manifold Leak
The VQ35DE's rear exhaust manifold operates in a confined space against the firewall. Gasket deterioration and broken manifold studs are common issues that create exhaust leaks. A leak here introduces extra air that confuses the downstream O2 sensor.
4. Engine Running Rich
Fuel injector problems, a failing mass air flow sensor, or a stuck purge valve can cause the engine to run rich. Excess fuel overwhelms the converter's ability to process it, reducing efficiency and triggering P0420.
How to Diagnose the Problem
- Scan for companion codes — Check for O2 sensor, fuel trim, and misfire codes alongside P0420.
- Monitor O2 sensor live data — Steady downstream voltage means a good converter. Oscillating voltage means it is failing.
- Inspect the exhaust system — Check the rear manifold for staining, broken studs, and listen for cold-start ticking.
- Check fuel trims — Abnormal long-term fuel trims indicate a fueling problem.
- Temperature test — Converter outlet should be 50-100°F hotter than inlet.
Repair Options
Professional Repair
A Nissan dealer or qualified independent shop can diagnose for $100-$150. The rear bank converter on the Murano requires some disassembly to access. OEM and aftermarket converters are available. Expect a full day of labor for converter replacement on the rear bank.
DIY Repair
O2 sensor replacement is achievable for experienced DIYers with the right tools. Converter replacement is challenging on the Murano due to limited rear bank access. Unless you are comfortable working in tight spaces, this is best left to a shop.
Estimated Repair Costs
- Catalytic converter replacement: $650 - $1,500
- Downstream O2 sensor: $125 - $300
- Exhaust manifold repair: $250 - $600
- Fuel system repair: $100 - $400
Prevention Tips
- Use quality fuel to protect the converter
- Address engine misfires and rough running immediately
- Keep up with spark plug replacements
- Inspect the exhaust system during oil changes
- Avoid excessive short trips that prevent the converter from fully warming up