What does code P0420 mean on a Chevrolet and is it safe to drive?
P0420: Catalyst System Efficiency Below Threshold (Bank 1). Here's what it means on your Chevrolet, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
What this code means
The downstream oxygen sensor detects that the catalytic converter is not storing or converting exhaust properly. This is one of the most common check engine codes.
Common causes for your Chevrolet
- Failed or aging catalytic converter
- Faulty downstream oxygen sensor
- Exhaust leak before or after the catalyst
- Engine misfire or rich/lean condition damaging the catalyst
Symptoms
- Check Engine Light on
- Often no drivability issues
- Possible failed emissions test
- Rotten egg smell in some cases
Typical fixes
- Replace catalytic converter
- Replace oxygen sensor(s)
- Repair exhaust leaks
- Fix underlying fuel/ignition issues first
Repair cost range
For a Chevrolet, repairs for P0420 often fall between $400 and $2400, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Chevrolet
Chevrolet P0420 on the 5.3L V8 is heavily linked to AFM (Active Fuel Management) lifter failures—a misfiring cylinder from a collapsed lifter dumps unburned fuel into the exhaust and destroys the cat quickly. Fix AFM issues first. On Equinox 2.4L (2010–2017), oil consumption via piston rings is a known defect that poisons the catalyst; GM issued a settlement on this. Cruze 1.4T has a small close-coupled cat that clogs early on high-mileage engines with oil consumption.
Most commonly affected models