2006 Hyundai P0420: What It Means & Is It Safe to Drive?
P0420 on the 2006 Hyundai: Catalyst System Efficiency Below Threshold (Bank 1). Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe 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 on the 2006 Hyundai
- 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 2006 Hyundai, repairs for P0420 typically fall between $400 and $2400, depending on the root cause and labor rates in your area.
Known issues on Hyundai
Hyundai P0420 on Theta II 2.4L engines is frequently tied to the oil consumption/rod bearing recall issue (2011–2019). Burning oil destroys the catalyst prematurely—confirm engine oil consumption is not excessive before replacing the converter. Hyundai extended the powertrain warranty on many Theta II vehicles; check if your VIN is covered at recalls.hyundai.com. On Elantra 2.0L NU engine, the downstream O2 sensor can give erratic readings if the exhaust flex pipe has a small leak near the sensor.
Most commonly affected models