Number P0430: Catalyst System Efficiency Below Threshold Bank 2
Like P0420, but for the catalyst of bank 2, so only on V and boxer engines with one catalyst per bank; Y-pipe systems with a shared catalyst report P0420 only. The module compares the oxygen sensors before and after the bank 2 catalyst – a good catalyst smooths the rear signal. GM checks on overrun
Can you drive with P0430?
Severity: Plan the repair. Yes — this is an emissions-system fault. The car will generally drive normally, but it will fail an emissions inspection with the light on.
If you ignore it: Fuel economy and emissions creep up, and some faults in this family (rich/lean running) stress the catalyst over time.
This is the #2 most common code in our top-150 library, in the catalyst & exhaust efficiency family (Powertrain system). Severity is Number Nest's editorial triage — if the light is flashing or the car feels unsafe, stop driving it whatever any page says.
What P0430 means
Like P0420, but for the catalyst of bank 2, so only on V and boxer engines with one catalyst per bank; Y-pipe systems with a shared catalyst report P0420 only. The module compares the oxygen sensors before and after the bank 2 catalyst – a good catalyst smooths the rear signal. GM checks on overrun and sets the code on the first trip if the ratio falls below 0.35; Ford evaluates an index ratio or fuel integration and usually needs several trips. The monitor only runs warm, in closed loop and without misfire, fuel or sensor faults.
Systems involved: catalytic converter, downstream oxygen sensor, upstream oxygen sensor, engine control module (ECM/PCM).
Causes, ranked by likelihood
| # | Cause | Likelihood |
|---|---|---|
| 1 | Catalyst aged or poisoned (oil consumption, silicone, coolant) | most likely |
| 2 | Catalyst overheated by misfire or rich running | possible |
| 3 | Rear oxygen sensor sluggish, dirty or unsuitable | possible |
| 4 | Exhaust leak ahead of or at the rear sensor | possible |
Check them in order — the list is ranked so the likely, cheaper causes come before the expensive part.
Symptoms you may notice
- Check engine light on, otherwise often no change in driving
- Emission test failed (higher HC, CO, NOx)
- Rattling or loss of power if the catalyst has broken up
Misdiagnosis traps
- Bank 2 on a V engine is the side WITHOUT cylinder #1 — misidentifying the bank replaces the good converter.
- A single-bank code with a healthy sensor usually means that bank's converter; a code on both banks at once points upstream (fuel, ignition, oil consumption).
How a good shop confirms it
- Confirm which side is bank 2 on your engine, then compare the downstream sensor signal against bank 1.
- Rule out leaks, sensor faults and engine causes before quoting the converter.
Repair options & costs
| Repair | Shop total (parts + labor) | DIY (parts only) | Difficulty |
|---|---|---|---|
| Oxygen sensor — downstream (post-cat) | $110 – $305 | $60 – $180 (parts only) | 2/5 |
| Catalytic converter replacement | $850 – $1,913 | $700 – $1,600 (parts only) | 4/5 |
National ranges from Number Nest's cost model (midsize car, independent shop, US-average labor). Published cross-check — Oxygen sensor — downstream (post-cat): CarMD 2026 national average $287; Catalytic converter replacement: CarMD 2026 national average $1,511.
OBDex repair data for this code rates the job difficulty medium with a typical labor time in the 0.5–3 hour range and DIY possible: yes.
Price this repair in your state
Estimated total: — (midsize car, independent shop)
Check the federal emissions warranty first
Before you pay: federal law (the Clean Air Act emissions warranty) requires the manufacturer to cover the catalytic converter and the engine computer (PCM) for 8 years or 80,000 miles on 1995-and-newer cars, whichever comes first. California-emissions (CARB) states cover a longer list of parts for 7 years/70,000 miles, and PZEV-rated vehicles sold in CARB states carry 15-year/150,000-mile emissions coverage on many components. Check your warranty booklet or a dealer lookup before authorizing this repair out of pocket.
Frequently asked questions
P0420 vs P0430 — what is the difference?
The bank. P0420 reports bank 1's converter, P0430 bank 2's. Inline engines have one bank; V engines have two converters and can set either code — or both, which usually points to a shared engine cause rather than two dead converters.
Can I just replace both converters to be done?
You can, but if the root cause is oil consumption, misfiring or rich running, the new converters will fail the same way. Fix the cause first.
How much does it cost to fix P0430?
The fix most associated with this code — oxygen sensor — downstream (post-cat) — runs $110 – $305 at an independent shop for a midsize car in our cost model (parts + labor, US average). The code names a system, not a part, so confirm the cause before spending: the ranked causes above are ordered by likelihood.
Can I drive with P0430?
See the can-you-drive verdict above — it is based on the system involved and the cascading-damage risk, and it is our editorial triage, not a manufacturer instruction. If the light is flashing or the car feels unsafe, stop driving it regardless of any code.
Will P0430 clear itself?
If the fault was a one-off (a loose cap, a cold-start glitch), the light can go out after several clean trips and the code ages into history. A fault that is still present re-sets the code as soon as the car runs that self-test again — monitors run under specific conditions, which is why "it hasn't come back in two days" is not proof of a fix.
Will my car fail inspection with P0430?
In states with OBD-based emissions inspection, yes — an illuminated check-engine light or an incomplete readiness monitor fails the test regardless of what the tailpipe would show. C-codes (ABS) fall under safety inspection instead in states that have one.
What should I check first for P0430?
The first item on the ranked-causes list above — it is ranked likelihood-first for exactly this reason — plus the free checks: recent work in the area (connectors left loose are a classic), fluid levels, and the battery and grounds on electrical codes.
Where this data comes from
Code facts, causes and symptoms come from OBDex — an open dataset of independently authored descriptions of the standardized generic OBD-II codes (CC0 1.0, public domain; github.com/foerbsnavi/OBDex). The SAE J2012 document itself is copyrighted and is not reproduced here. Cost ranges are Number Nest's own US planning model: national parts and labor ranges cross-checked against the CarMD Vehicle Health Index 2026 published averages, with labor adjustable by the BLS OEWS May 2025 state wage index for auto technicians (occupation 49-3023) — a wage index, not a surveyed shop rate. Severity and can-you-drive notes are our editorial triage, not a manufacturer instruction.