Failed or under-performing Bank 2 catalytic converter (both sources). An oxygen sensor not reading properly (OBD-Codes.com). Exhaust leak (OBD-Codes.com). Internal engine damage causing high oil consumption, or a leaking head gasket, that has damaged the converter (RepairPal). Engine misfire that has damaged the converter (RepairPal).

Repair exhaust leaks. Replace a faulty O2 sensor or repair its wiring. Fix the underlying engine problem (misfire, oil consumption, head gasket leak). Replace the Bank 2 catalytic converter once other causes are ruled out.

P0430🌫 Emissions / exhaustDrive with caution, fix soon

P0430: Catalyst System Efficiency Below Threshold (Bank 2) (Meaning, Causes, Fixes)

Q: What does P0430 mean?

P0430 is the Bank 2 version of P0420: the engine computer thinks the catalytic converter on the side of the engine without cylinder #1 isn't cleaning the exhaust as well as it should. It only appears on engines with two banks (V6, V8 and similar). Check for exhaust leaks, O2 sensor faults and engine problems before buying a converter. The PCM compares the oxygen (O2) sensor in front of the Bank 2 catalytic converter with the monitoring sensor behind it. A working converter smooths out the exhaust, so the rear sensor's reading stays fairly steady while the front one swings. RepairPal explains that if the rear sensor's input starts to match the front sensor, the PCM decides the converter's efficiency has fallen below the minimum allowable threshold and sets P0430. Bank 2 is the side of the engine opposite cylinder #1. RepairPal notes converters usually fail because something else, such as an engine misfire or an internal oil or coolant leak, wasn't repaired.

Q: Can I keep driving with P0430?

Drive with caution, fix soon. Usually you can keep driving short-term: OBD-Codes.com says you likely won't notice drivability problems. But don't ignore it. A converter that's breaking up can restrict the exhaust (RepairPal lists a noticeable lack of power in some cases), and a misfire or oil or coolant burning that's damaging it should be fixed first. If the check engine light is flashing, stop driving soon. Sources differ on urgency: RepairPal rates P0430 'Urgent', while OBD-Codes.com says most drivers won't notice drivability problems. We treat it as 'fix soon', not as an emergency.

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0430 means

The PCM compares the oxygen (O2) sensor in front of the Bank 2 catalytic converter with the monitoring sensor behind it. A working converter smooths out the exhaust, so the rear sensor's reading stays fairly steady while the front one swings. RepairPal explains that if the rear sensor's input starts to match the front sensor, the PCM decides the converter's efficiency has fallen below the minimum allowable threshold and sets P0430. Bank 2 is the side of the engine opposite cylinder #1. RepairPal notes converters usually fail because something else, such as an engine misfire or an internal oil or coolant leak, wasn't repaired.

Severity: can I keep driving?

Drive with caution, fix soon

Usually you can keep driving short-term: OBD-Codes.com says you likely won't notice drivability problems. But don't ignore it. A converter that's breaking up can restrict the exhaust (RepairPal lists a noticeable lack of power in some cases), and a misfire or oil or coolant burning that's damaging it should be fixed first. If the check engine light is flashing, stop driving soon. Sources differ on urgency: RepairPal rates P0430 'Urgent', while OBD-Codes.com says most drivers won't notice drivability problems. We treat it as 'fix soon', not as an emergency.

Common symptoms

Check engine light on (often the only symptom)
In many cases, no other abnormal symptoms (both sources)
Noticeable lack of engine power in some cases (RepairPal)
Rough or hard idle when cold in some cases (OBD-Codes.com)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Failed or under-performing Bank 2 catalytic converter (both sources)
An oxygen sensor not reading properly (OBD-Codes.com)
Exhaust leak (OBD-Codes.com)
Internal engine damage causing high oil consumption, or a leaking head gasket, that has damaged the converter (RepairPal)
Engine misfire that has damaged the converter (RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes. If misfire codes (P0300–P0308) or fuel trim codes (P0171/P0174) are present, fix those first; they can damage the converter.
Inspect the exhaust for leaks, which OBD-Codes.com lists as the first step.
Check the O2 sensors on Bank 2. OBD-Codes.com suggests measuring the Bank 2 sensor voltage and testing each O2 sensor while you're at it. A scanner with live data lets you compare the front and rear readings on a warm engine.
If you also have P0420, both converters are being flagged, which makes an engine problem (misfire, oil or coolant burning) more likely to be the root cause.

Typical fixes

Repair exhaust leaks
Replace a faulty O2 sensor or repair its wiring
Fix the underlying engine problem (misfire, oil consumption, head gasket leak)
Replace the Bank 2 catalytic converter once other causes are ruled out

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

Confirming O2 sensor operation properly needs an advanced scan tool
The converter needs replacing (welding, emissions legality)
You suspect internal engine damage such as oil burning or a head gasket leak
Your car may still be under an emissions-parts warranty; ask a dealer before paying for a converter

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Should I replace the O2 sensor first?

RepairPal lists replacing O2 sensors when the real problem is a damaged catalyst as a common misdiagnosis, along with replacing the catalyst when the real problem is a misfire or internal engine damage. Diagnose first.

Is the converter covered by warranty?

The sources describe this differently. RepairPal says catalytic converters are covered under a federally mandated 8-year/80,000-mile manufacturer warranty, but the original cause of the failure (like a misfire) usually isn't. OBD-Codes.com says many manufacturers give a five-year, unlimited-mileage warranty on emissions parts. Coverage depends on your vehicle and state, so have a dealer check your VIN.

What's the difference between P0430 and P0420?

They're the same test on different sides of the engine. P0420 is Bank 1 (the side with cylinder #1) and P0430 is Bank 2, which only exists on V-type and other two-bank engines.

Sources

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.