P0430 means the catalytic converter on bank 2 is not cleaning the exhaust as efficiently as the engine management expects — the exact same fault as P0420, just on the other bank. Follow the identical diagnostic process: a worn converter is responsible about half the time, and an exhaust leak or a lazy downstream oxygen sensor explains most of the rest.
What Does P0430 Mean?
P0430 is Catalyst System Efficiency Below Threshold (Bank 2) — identical in principle to P0420. The ECU compares the oxygen sensor readings before and after the bank 2 converter; a healthy converter smooths out the signal, and when the downstream reading starts mirroring the upstream one, the converter is judged to have stopped buffering oxygen effectively.
Only engines with two exhaust banks and two converters — most V6 and V8 layouts — can report this code specifically. See our full P0420 guide for the detailed explanation of the sensor comparison, which applies identically here.
Common Symptoms
- Check engine light on, steady — often the only symptom.
- Failed emissions test.
- A sulphur smell from the exhaust under load — see our rotten egg smell guide if this is prominent.
- Mild power loss or a rattle if the converter has broken up internally.
Common Causes (Same Order as P0420)
- A worn-out catalytic converter on bank 2 — the most likely cause if nothing else checks out, especially on a higher-mileage car.
- An exhaust leak near the bank 2 sensors, letting fresh air skew the downstream reading.
- A failing downstream oxygen sensor on bank 2.
- An engine running rich or lean on that bank — check for P0171‘s bank-2 twin, P0174, or fix fuel-trim issues first.
- Misfires on a bank 2 cylinder, which cook the converter from unburned fuel.
- Oil or coolant burning on that bank contaminating the converter.
How to Diagnose It
The process is identical to P0420, applied to bank 2’s sensors and converter:
- Read every code first — a bank 2 misfire or fuel-trim code takes priority.
- Inspect the bank 2 exhaust for leaks near the sensors.
- Compare bank 2’s upstream and downstream oxygen sensor traces with a scan tool showing live data.
- Check for a temperature difference across the bank 2 converter with an infrared thermometer.
Never work under a vehicle supported only by a jack. Use axle stands on firm, level ground, chock the wheels that stay down, and leave the car in gear or Park with the handbrake on. A jack lifts; stands hold.
Possible Fixes
| Cause | Fix | Typical cost |
|---|---|---|
| Exhaust leak, bank 2 | Weld or replace the section, renew gaskets | $150 – $400 |
| Failed downstream O2 sensor, bank 2 | Replace the sensor | $150 – $350 |
| Rich/lean running on bank 2 | Fix the underlying fuel/air fault | $100 – $600 |
| Worn-out converter, bank 2 | Replace the converter | $500 – $2,400 |
Can I Drive With P0430?
Yes, in almost all cases — like P0420, this is an emissions fault rather than a mechanical or safety one, and the car will drive normally. You will fail an emissions test until it is resolved, and a rattle from a breaking-up converter is worth checking promptly since debris can restrict the exhaust.
When to See a Mechanic
Not urgent unless accompanied by misfires, a flashing check engine light, or a rattling exhaust. Mention whether P0420 is present as well — both at once often means a shared upstream cause rather than two independently worn converters. More in our trouble codes section.
Frequently Asked Questions
What is the difference between P0420 and P0430?
Only which bank reported it. P0420 is bank 1, P0430 is bank 2 — only engines with two exhaust banks and two converters, mostly V6 and V8 layouts, can set P0430.
Does P0430 always mean I need a new catalytic converter?
No — confirm with live oxygen sensor data first. An exhaust leak or a failing downstream sensor produces the same code for a fraction of the cost of a converter.
Can I drive with a P0430 code?
Yes, almost always. It is an emissions fault rather than a safety one, though the car will fail an emissions test until it is resolved.
What causes P0430?
The same list as P0420, applied to bank 2: most often a worn converter, followed by an exhaust leak or a failing downstream oxygen sensor near that bank.
How much does it cost to fix P0430?
From $150 for an exhaust leak repair to $500 – $2,400 for a full converter replacement on that bank, depending on the vehicle.
