P0420 on a Nissan: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

You can usually keep driving a Nissan short-term with P0420, but a failing converter will eventually hurt fuel economy and power.

What P0420 means on a Nissan

On a Nissan, P0420 means the downstream oxygen sensor on bank 1 tells the ECM the catalytic converter isn't doing its job. Nissan's computer compares the front and rear O2 sensors and flags the converter when the readings get too similar. Most Nissan four-cylinders have a single bank, so this code covers the one converter.

Is P0420 common on Nissans?

P0420 appears often on Altimas, Rogues, and Sentras, especially past 100,000 miles. Nissan's 2.5L engines are known for MAF sensor issues that upset the air-fuel mix, which can shorten converter life, and the rear O2 sensor itself is a frequent failure point.

Commonly reported on: Altima, Rogue, Sentra, Pathfinder.

Symptoms

Check engine light on
Slightly worse fuel economy
Rotten-egg smell from the exhaust
Usually no change in how it drives

Common causes

most common: Worn catalytic converter
common: Faulty rear oxygen sensor (sensor 2)
common: Dirty or failing MAF sensor hurting the air-fuel mix
less common: Exhaust leak before the rear sensor

How to fix it

Fix	DIY?	Typical cost
Check the exhaust for leaks and repair them first	Yes	$50–200
Test the rear oxygen sensor and replace it if faulty	Yes	$60–200
Clean the MAF sensor with MAF cleaner	Yes	$10–20
Replace the catalytic converter	Mechanic	$600–2200

Frequently asked questions

Can I drive my Nissan with P0420?

Yes, usually for a short time. The car will keep running, but a failing converter can reduce fuel economy and eventually clog, so get it checked soon.

Why do Nissan 2.5L engines get P0420?

The 2.5L engine in Altimas, Rogues, and Sentras is prone to MAF sensor problems that make the fuel mix run off, which can shorten converter life. The rear O2 sensor is also a common failure.

How much does it cost to fix P0420 on a Nissan?

A rear O2 sensor runs about $60–$200, a MAF sensor about $100–$300, and a converter replacement typically $600–$2,200.