P0420 on a Volvo: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

A Volvo with P0420 can usually be driven short-term, but a failing converter will eventually hurt fuel economy.

What P0420 means on a Volvo

On a Volvo, P0420 means the rear oxygen sensor on bank 1 reports the catalytic converter isn't cleaning the exhaust as well as it should. Volvo's computer compares the front and rear O2 sensors, and when they stay too similar it stores the code. On four-cylinder models there's a single bank, so the code covers the one converter.

Is P0420 common on Volvos?

P0420 is common on higher-mileage XC90s, XC60s, and S60s. Volvo oxygen sensors wear with age, and some 2.0L engines have enough oil consumption to shorten catalytic converter life.

Commonly reported on: XC90, XC60, S60, S90.

Symptoms

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

Common causes

most common: Worn catalytic converter
common: Faulty rear oxygen sensor
common: Exhaust leak before the rear sensor
less common: Oil consumption from the engine contaminating the converter

How to fix it

Fix	DIY?	Typical cost
Check for exhaust leaks and repair them first	Yes	$50–200
Test and replace the rear oxygen sensor if faulty	Yes	$80–240
Replace the catalytic converter	Mechanic	$800–2600

Frequently asked questions

Can I drive my Volvo with P0420?

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

Do Volvos get P0420 from a sensor or the converter?

Both are common. Higher-mileage Volvos often wear out the rear O2 sensor, and engines that use oil can damage the converter, so a shop should test before replacing parts.

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

A rear O2 sensor is about $80–$240, while a converter replacement is typically $800–$2,600 depending on the model.