Emission controls · Powertrain · generic (SAE-defined)
P0430: Catalyst System Efficiency Below Threshold (Bank 2)
P0430 means the engine computer has found that the catalytic converter on Bank 2, the side of a V6 or V8 opposite cylinder 1, is not cleaning the exhaust as well as required.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0430 sets
The powertrain control module (PCM) watches the upstream oxygen sensor (Bank 2 Sensor 1) and the downstream oxygen sensor (Bank 2 Sensor 2). A working converter stores oxygen, so the downstream sensor normally shows a steadier signal than the rapidly switching upstream sensor. When the downstream sensor begins to follow the upstream switching closely during a warm, steady-driving test, the PCM concludes the converter's oxygen storage has dropped and sets P0430. The test conditions and threshold are manufacturer-specific.
Common causes of P0430
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Aged or failed Bank 2 catalytic converter
- Converter damage caused by misfires, oil burning, coolant leaks, or rich running
- Exhaust leak near the Bank 2 oxygen sensors
- Slow or failed downstream oxygen sensor (Bank 2 Sensor 2)
- Faulty upstream sensor affecting Bank 2 fuel control
- Leaking fuel injector on Bank 2
- Non-compliant or low-quality replacement converter
P0430 symptoms
- Check engine light on
- Frequently no drivability symptoms
- Sulfur or rotten-egg exhaust odor
- Sluggish acceleration or lower fuel economy if the converter is restricted
- Failed emissions inspection
How P0430 is diagnosed
- Read all codes and freeze frame data; resolve misfire, fuel trim, and oxygen sensor codes on Bank 2 before replacing the converter
- Confirm which side of the engine is Bank 2 (the side without cylinder 1) using service information
- Inspect for exhaust leaks at the manifold, gaskets, flex joints, and around the downstream sensor
- Compare Bank 2 fuel trims with Bank 1; a large difference suggests a fuel or misfire problem specific to Bank 2
- Graph upstream and downstream Bank 2 sensor signals at a warm, steady cruise
- Verify downstream sensor response with a rich/lean test; a lazy sensor can mimic a failed converter
- Check for oil consumption, coolant loss, and available PCM software updates
Typical fixes for P0430
- Fix the root cause first: misfires, oil burning, coolant leaks, or a rich-running condition
- Repair any exhaust leak upstream of or near the downstream sensor
- Replace the downstream or upstream Bank 2 oxygen sensor if it fails testing
- Replace the Bank 2 catalytic converter with a unit certified for the vehicle
- Install a manufacturer software update if available
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Applies only to engines with two banks, such as V6 and V8 engines. Commonly reported on higher-mileage trucks and SUVs from many manufacturers; definitions can vary by manufacturer, so check factory service information.
Related codes & warning lights
P0430 FAQ
What does code P0430 mean?
P0430 means the engine computer has found that the catalytic converter on Bank 2, the side of a V6 or V8 opposite cylinder 1, is not cleaning the exhaust as well as required. The standard definition is "Catalyst System Efficiency Below Threshold (Bank 2)."
Can I drive with a P0430 code?
Usually yes, provided the engine runs smoothly and the check engine light is not flashing. If you notice misfiring, a flashing light, a drop in power, or a strong sulfur smell, cut back on driving, since the underlying problem may be overheating or clogging the converter.
Why do I have P0430 but not P0420?
Each bank has its own converter, or its own section of a converter, and they wear independently. A misfire, injector leak, or exhaust leak on only one side of the engine can damage or mislead the monitor on that side alone.
Should I replace the oxygen sensor or the converter first?
Test before replacing either. If the downstream sensor responds quickly and there are no exhaust leaks, the converter is the likely fault. A slow downstream sensor or a leak can make a good converter look bad.
Can I fix P0430 by replacing only the Bank 2 converter?
Often yes, if the converter is a separate part on that side and the root cause has been corrected. On some vehicles both banks feed a shared converter or Y-pipe assembly.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.