What does code P0420 mean and is it safe to drive?
P0420: Catalyst System Efficiency Below Threshold (Bank 1). Here’s what it means, what usually causes it, what repairs typically cost, and how urgent it is to keep driving.
PowertrainGenerally safe to drive
Repair cost
$400–$2400
System
Powertrain
Urgency
medium
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
- 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
Repairs for P0420 often fall between $400 and $2400, depending on the cause and your vehicle.