P0420 on Lexus: 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 Lexus
Lexus vehicles share Toyota engines, and P0420 shows up mostly at high mileage. V6 and V8 Lexus models may have multiple converters, so P0430 can appear too.
Most likely causes on Lexus vehicles
- Exhaust leak
- Rear oxygen sensor
- Worn converter
Order reflects cost and likelihood in general; your vehicle may differ. Confirm with testing before buying parts.
Lexus specific tips
- Check the emissions warranty if eligible.
- Use quality parts; Lexus systems are sensitive to cheap converters.
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 Lexus 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 Lexus fix” videos.
Repair manuals
Step-by-step service manuals for Lexus with torque specs and wiring diagrams:
Haynes manuals for Lexus Chilton manuals
Affiliate disclosure: links in this box may earn FixOrPark a commission at no extra cost to you.
Check Lexus recalls
Enter your VIN at the NHTSA recall lookup before paying for repairs.
FAQ
Does Lexus use the same converters as Toyota?
Often similar, but always match the exact part for your vehicle.
Read the full P0420 guide or more Lexus check engine notes.