P0420 on Hyundai: Catalyst System Efficiency Below Threshold (Bank 1)
Severity: 2 of 4
Usually safe to drive for a short time if the light is steady and the car runs normally. Fix the cause before it gets worse, because a converter that is overheating from misfires can become a fire risk and will fail completely. If the light flashes, or you smell strong sulfur or see a glowing red converter, park it.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0420 usually means on a Hyundai
Hyundai models commonly set P0420. Because some Hyundai engines are covered by recalls and extended warranties for connecting rod bearing failure, oil consumption should be checked alongside catalyst health.
Most likely causes on Hyundai vehicles
- Exhaust leak
- Rear oxygen sensor
- Oil consumption
- Worn converter
Order reflects cost and likelihood in general; your vehicle may differ. Confirm with testing before buying parts.
Hyundai specific tips
- Check NHTSA recalls and Hyundai warranty extensions.
- Keep oil change records; they help with warranty claims.
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Rear oxygen sensor | $30 to $120 | 0.3 to 1.0 h | $30 + 0.3 × $110 = $63 $120 + 1.0 × $190 = $310 |
| Exhaust gasket or flex pipe repair | $15 to $150 | 0.5 to 1.5 h | $15 + 0.5 × $110 = $70 $150 + 1.5 × $190 = $435 |
| Catalytic converter (aftermarket, direct fit) | $250 to $1,400 | 1.0 to 2.5 h | $250 + 1.0 × $110 = $360 $1,400 + 2.5 × $190 = $1,875 |
Costs are generic for this code; parts and labor on some Hyundai models may run higher.
Watch a repair video
P0420 How To Diagnose A Bad Catalytic Converter (EricTheCarGuy). Third-party video, loads from YouTube (privacy-enhanced mode) only when you press play. Procedures vary by vehicle. Search YouTube for “P0420 Hyundai fix” videos.
Repair manuals
Step-by-step service manuals for Hyundai with torque specs and wiring diagrams:
Haynes manuals for Hyundai Chilton manuals
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Check Hyundai recalls
Enter your VIN at the NHTSA recall lookup before paying for repairs.
FAQ
Does Hyundai cover catalytic converters?
Federal emissions warranty coverage applies; check your booklet for specifics.
Read the full P0420 guide or more Hyundai check engine notes.