P0420 on a Chevy: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

A Chevy with P0420 can usually be driven short-term, but ignoring it can lead to worse fuel economy and a clogged converter.

What P0420 means on a Chevy

On a Chevy, P0420 means the rear oxygen sensor on bank 1 says the catalytic converter isn't cleaning the exhaust efficiently. The ECM compares front and rear O2 readings, and when they match too closely it sets the code. On V8 trucks, bank 1 is the driver's side.

Is P0420 common on Chevys?

P0420 is a frequent complaint on Silverados, Tahoes, and Equinoxes with higher mileage. On Chevy V8s, intake manifold gasket leaks and misfires are a known route to a damaged converter, so the root cause is worth checking before replacing parts.

Commonly reported on: Silverado, Equinox, Malibu, Tahoe.

Symptoms

Check engine light on
Slightly worse fuel economy
Rotten-egg smell from the exhaust
Possible rough idle from an underlying misfire

Common causes

most common: Worn catalytic converter on bank 1
common: Faulty rear oxygen sensor
common: Exhaust leak before the rear sensor
less common: Misfire from an intake gasket leak or ignition issue that poisoned the converter

How to fix it

Fix	DIY?	Typical cost
Look for exhaust leaks and repair them before replacing parts	Yes	$50–200
Test the rear oxygen sensor and replace it if it's faulty	Yes	$60–200
Replace the catalytic converter on bank 1	Mechanic	$600–2400

Frequently asked questions

Can I drive my Chevy with a P0420 code?

Yes for a short time, but it's best to diagnose it soon. A failing converter hurts fuel economy, and if a misfire caused the code, driving on it can damage the converter further.

Why do Chevy trucks get P0420 so often?

Higher-mileage Silverados and Tahoes commonly wear out the bank 1 converter, and intake gasket leaks that cause misfires can damage it faster, so the fix often starts with the gasket.

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

A rear O2 sensor is about $60–$200, while a converter replacement is typically $600–$2,400. If an intake gasket leak caused it, that repair adds a few hundred dollars.