What does P0430 mean?
The computer compares the oxygen sensors before and after the catalytic converter. A healthy converter stores oxygen, so the downstream sensor should stay fairly steady. When the downstream signal starts copying the upstream one, the computer decides the converter on bank 2 is not cleaning the exhaust well enough.
Codes are a starting point. They tell you which test failed, not which part to replace. Check for other stored codes and fix those in a sensible order.
Symptoms
- Check engine light
- Usually no noticeable change in how the car drives
- Possible rotten egg smell
- Failed emissions test
- Loss of power only if the converter is physically clogged
Common causes
- Worn-out catalytic converter (common past 100,000 miles)
- Exhaust leak near the downstream O2 sensor
- Lazy or failing downstream oxygen sensor
- Misfires or oil burning that damaged the converter
- Engine running rich over time
How to diagnose P0430
- Check for misfire, fuel trim and O2 sensor codes first. Fix those before blaming the converter.
- Look at the downstream O2 sensor at a steady 2,500 rpm when fully warm. It should stay steady around 0.5 to 0.8 V. If it switches as fast as the upstream sensor, the converter is likely worn.
- Check for exhaust leaks around the sensors and flanges.
- Check for a software update (TSB) for your vehicle before buying a converter.
How to fix it
- Repair exhaust leaks
- Fix misfires or rich running first
- Replace a faulty downstream O2 sensor
- Replace the catalytic converter (use a CARB-compliant one in California and other CARB states)
Estimated repair cost
Likely repairs for P0430 run from about $100 to $3,500, depending on the cause.
| Repair | Typical range (parts + labor) |
|---|---|
| Diagnostic fee (scan + testing) | $100 - $200 |
| Oxygen / A/F sensor replacement | $150 - $450 |
| Exhaust leak repair (gasket/flange) | $100 - $400 |
| Catalytic converter (aftermarket, direct fit) | $900 - $2,500 |
| Catalytic converter (OE or CARB-legal) | $1,500 - $3,500 |
These are rough US estimates for an independent shop in 2026, based on typical parts prices and standard labor times. Dealers, big trucks, luxury brands and high-cost areas often run higher. They are not quotes. Use the repair cost estimator to adjust for your vehicle.
How serious is P0430?
Moderate severity
Usually safe to drive in the short term. Do not ignore a flashing check engine light or a red-hot converter, which means misfires are destroying it.
Make-specific notes
Toyota / Lexus
On V6 and V8 Toyotas, bank 2 is the side without cylinder 1. Check the bank 2 downstream sensor and its connector before buying a converter.
Always check open recalls and technical service bulletins for your VIN.
P0430 FAQ
What is the difference between P0420 and P0430?
They mean the same thing, just on different sides of a V engine. P0420 is bank 1 (the side with cylinder 1), and P0430 is bank 2.
Is the catalytic converter covered by warranty?
Federal law covers the catalytic converter on 1995 and newer light-duty vehicles for 8 years or 80,000 miles.
What does P0430 mean?
P0430 stands for "Catalyst System Efficiency Below Threshold (Bank 2)". The computer compares the oxygen sensors before and after the catalytic converter.
Can I drive with a P0430 code?
Usually safe to drive in the short term. Do not ignore a flashing check engine light or a red-hot converter, which means misfires are destroying it.
How much does it cost to fix P0430?
It depends on the cause. The likely repairs for P0430 range from about $100 to $3,500 at an independent shop in the US, plus a diagnostic fee of roughly $100-$200. These are rough estimates; dealer prices and some vehicles run higher.