All codes › P0420
P0420: Catalyst System Efficiency Below Threshold (Bank 1)
What it means
The bank 1 catalytic converter isn't cleaning the exhaust as well as it should, based on the downstream O2 sensor.
Severity: Medium Usually drives fine, but will fail emissions; fix misfires first.
Common causes
- Worn-out catalytic converter
- Faulty downstream O2 sensor
- Exhaust leak near sensors
- Misfires or oil burning that damaged the cat
Most common causes first. Exact causes vary by make, model and engine.
Can I fix it myself?
Rarely DIY. Confirm the downstream O2 sensor first; converter must be EPA/CARB legal for your state.
Repair cost
SEEDED ESTIMATE Roughly $570–$1460
Most likely repair: catalytic converter. Diagnosis fees, taxes and other causes are not included.
| Line | Low | High | Basis |
|---|---|---|---|
| Catalytic converter | $468 | $1063 | Typical listed retail range, source |
| Labor 1–2.5 hr | $100 | $400 | $100–$160/hr, shop survey |
⚠️ This is an editorial placeholder range for this type of repair. It is not based on real invoices or licensed pricing data yet. Real ranges will appear here once enough reader invoices for P0420 are verified.
Verified reader invoices for P0420: 0. Share your repair bill to help build real costs.
Tools that can read P0420
- ScanFixAI: Pro $29.99/mo or $249.99/yr
- OBDAI: Annual PRO bundle $299
- BlueDriver Pro Next-Gen: $119.95 list ($99.95 sale seen)
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