# P0430: Catalyst System Efficiency Below Threshold (Bank 2) **Verdict:** Drive to a shop this week Emissions - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $150-$2,800 - **Urgency:** This week - **Most likely:** Worn bank 2 converter or rear O2 sensor - **DIY?:** Steps 1-2 ## Quick answer P0430 means the engine computer has decided the catalytic converter on bank 2 is not cleaning the exhaust well enough. Bank 2 is the side of a V6 or V8 engine that does not have cylinder 1, so this code only appears on engines with two exhaust banks. Causes are the same family as P0420, a worn converter, an exhaust leak, or a lazy rear oxygen sensor, but on the other side of the engine. ## What does P0430 mean? P0430 is the bank 2 version of P0420. A V6, V8, or flat engine has two rows of cylinders, called banks, and many have a separate catalytic converter for each side. Bank 1 is the side that holds cylinder 1, so bank 2 is the opposite side. Which side that is depends on the engine, and it is not always the driver or passenger side you might guess. The computer tests the bank 2 converter by comparing its two oxygen sensors: bank 2 sensor 1 ahead of the converter, and bank 2 sensor 2 after it. A healthy converter stores oxygen, so the rear sensor stays fairly steady while the front sensor switches. When the rear reading starts copying the front, efficiency has dropped below the threshold. The test usually runs once per trip at steady cruise with a warm engine, and most cars light the check engine lamp after two failed trips. Engines whose two banks share a single converter usually report only P0420. ## What are the symptoms of P0430? - Check engine light on, car drives normally - Failed emissions test - Sulfur smell from the exhaust on some cars - Reduced power if the converter is clogged ## What causes P0430? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Worn-out bank 2 catalytic converter** (most common). The converter's precious-metal coating loses its ability to store oxygen with age, heat, and miles, usually after many years of service. Because both converters often see similar wear, P0420 may follow later. On a scan tool, the bank 2 rear oxygen sensor starts switching nearly as fast as the bank 2 front sensor. 2. **Exhaust leak on the bank 2 side** (common). A cracked bank 2 exhaust manifold, a failed manifold gasket, a leaking flex pipe, or loose flange bolts let outside air into the exhaust. That air confuses the oxygen sensors and can make a working converter look weak. Manifold cracks and broken studs are common on some V6 and V8 engines and often tick on cold starts. 3. **Failing bank 2 rear oxygen sensor** (common). A slow, contaminated, or aging bank 2 downstream oxygen sensor can falsely flag a good converter. Oil or coolant entering the exhaust on that bank shortens sensor life. Because the sensor costs far less than a converter, a shop should check its response and its wiring, which often runs near hot exhaust, before replacing the converter. 4. **Misfires or rich running on bank 2 cylinders** (less common). A misfiring cylinder on bank 2 sends unburned fuel into that bank's converter, where it burns and overheats the inside. A rich condition on that bank does the same thing more slowly. Look for misfire codes on the bank 2 cylinders and bank 2 fuel trim codes, since cylinder numbering differs between engine makers. ## How do you diagnose P0430? 1. Confirm which side of your engine is bank 2 (the side opposite cylinder 1). 2. Check for misfire codes on bank 2 cylinders and fuel trim codes such as P0174, and fix those first. 3. Look for exhaust leaks on the bank 2 side, especially near the oxygen sensors. 4. Compare bank 2 front and rear oxygen sensor readings at steady cruise. Check whether P0420 is also set, which can suggest a shared cause. ## How do you fix P0430, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Repair bank 2 exhaust leak | $100-$400 | Gaskets, flex pipe, or manifold repair. | | Replace bank 2 rear oxygen sensor | $150-$400 | A good first step if the sensor is old or tests slow. | | Replace bank 2 catalytic converter | $900-$2,800 | On some vehicles the bank 2 converter is built into the exhaust manifold, which costs more. | Full price breakdowns: [catalytic converter replacement cost](/cost/catalytic-converter-replacement), [oxygen sensor replacement cost](/cost/oxygen-sensor-replacement). ## Is it safe to drive with P0430? > **Drive to a shop this week.** It is usually safe to drive for a few weeks. Get it checked sooner if power drops, the exhaust smells strongly, or a misfire makes the check engine light flash. ## Will P0430 fail an emissions test? A stored P0430 with the check engine light on fails an OBD-based emissions test in most states, exactly like P0420. Clearing the code resets the catalyst monitor, which can take several days of mixed driving to rerun. In California and states that follow its rules, a replacement bank 2 converter must be CARB-approved for your vehicle. ## After the repair: clearing P0430 Clear the code after the repair and drive normally, with some steady highway cruising once the engine is warm. The catalyst monitor checks both banks and often needs several trips to finish. The fix worked when the monitor shows complete, no pending P0430 or P0420 appears, and the bank 2 rear sensor reads fairly steady. ## How to prevent P0430 - Fix misfires on bank 2 cylinders quickly, since each misfire sends raw fuel into that converter. - Address oil burning and coolant loss early, since both contaminate the converter on the affected bank. - Replace spark plugs and coils on schedule, including the hard-to-reach rear bank on transverse V6 engines. - Have a ticking bank 2 exhaust manifold leak repaired before it skews the oxygen sensor readings. - Investigate bank 2 fuel trim codes, such as P0174 or P0175, before they damage the converter. ## Codes often seen with P0430 - [P0420](/codes/p0420): Catalyst System Efficiency Below Threshold (Bank 1) - [P0300](/codes/p0300): Random/Multiple Cylinder Misfire Detected - [P0174](/codes/p0174): System Too Lean (Bank 2) - [P0175](/codes/p0175): System Too Rich (Bank 2) ## Frequently asked questions ### Can I drive with a P0430 code? Yes, you can usually drive normally for a while with P0430. Plan the repair before your next emissions test, and check for engine problems such as misfires that could make it worse. Get it seen right away if power drops, the exhaust smells strongly of sulfur, or the light flashes. ### What is bank 2? Bank 2 is the row of cylinders that does not contain cylinder 1 on a V-shaped or flat engine. Your service manual or a firing-order diagram will show which side that is. On many front-wheel-drive V6 cars, the banks face the front and rear of the car rather than left and right. ### Why do I have both P0420 and P0430? Both converters may be worn out from age, or one problem such as oil burning, a rich mixture, or misfires on both banks may be affecting both. Look for a shared engine problem before replacing both converters. Replacing only the converters can lead to both codes returning within months. ### How much does it cost to fix P0430? Most P0430 repairs cost $150 to $2,800 at an independent shop. A bank 2 exhaust leak repair runs about $100 to $400 and a bank 2 rear oxygen sensor $150 to $400. A new bank 2 converter costs $900 to $2,800, and manifold-mounted converters on some engines sit at the top. ### Will P0430 make me fail an emissions test? Yes, P0430 will fail an OBD-based emissions test in most states while the code is stored and the light is on. Clearing it does not help, because the catalyst monitor resets and needs several trips to rerun. Repair the cause, then drive until the monitor shows complete before going for a retest. ### Can I fix P0430 myself? You can do the first steps yourself, such as reading codes, checking for bank 2 exhaust leaks, and replacing the bank 2 rear oxygen sensor if it is reachable. On many transverse V6 engines the rear bank is cramped. Converter replacement usually needs a lift and rusted-bolt work, so most owners use a shop. ### Can I replace only the bank 2 catalytic converter? Yes, on engines with separate converters for each bank you can usually replace only the bank 2 converter if bank 1 tests fine. Some exhaust systems join both converters into one assembly, so both get replaced together. Ask the shop to confirm bank 1 is healthy before deciding. ### Is a bank 2 catalytic converter covered by warranty? Federal law requires catalytic converters to be covered for 8 years or 80,000 miles on most cars sold in the US, and that applies to each converter. California and some other states have longer coverage for some vehicles. Check your warranty booklet and bring your service records to the dealer. ### Where is the bank 2 rear oxygen sensor? The bank 2 rear oxygen sensor, labeled bank 2 sensor 2, sits in the exhaust pipe just after the bank 2 converter, on the side of the engine opposite cylinder 1. Some vehicles have a single rear sensor after a shared converter instead, and that sensor is usually called bank 1 sensor 2. ### Why do I have P0430 but not P0420? Each bank has its own converter and oxygen sensors, so one side can wear out or be damaged first. A misfire, exhaust leak, or rich condition limited to bank 2 cylinders would set only P0430. If the code started after a misfire or engine repair on that side, look there first. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other emissions codes - [P0411 Secondary Air Injection System "A" Incorrect Flow Detected](https://diagxcar.com/codes/p0411) - [P0420 Catalyst System Efficiency Below Threshold (Bank 1)](https://diagxcar.com/codes/p0420) - [P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)](https://diagxcar.com/codes/p0421) - [P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2)](https://diagxcar.com/codes/p0431) - [P0440 Evaporative Emission System](https://diagxcar.com/codes/p0440) - [P0441 Evaporative Emission System Incorrect Purge Flow](https://diagxcar.com/codes/p0441) - [P0442 Evaporative Emission System Leak Detected (small leak)](https://diagxcar.com/codes/p0442) - [P0443 Evaporative Emission System Purge Control Valve "A" Circuit](https://diagxcar.com/codes/p0443) - [P0446 Evaporative Emission System Vent Control Circuit](https://diagxcar.com/codes/p0446) - [P0449 Evaporative Emission System Vent Valve/Solenoid Circuit](https://diagxcar.com/codes/p0449) - [P0151 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0151) - [P0153 O2 Sensor Circuit Slow Response (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0153) - [P0156 O2 Sensor Circuit (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0156) - [P0157 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0157) ## Symptoms - [Why does my car smell like rotten eggs?](https://diagxcar.com/symptoms/car-smells-like-rotten-eggs) ## Repair costs - [Catalytic converter replacement cost](https://diagxcar.com/cost/catalytic-converter-replacement): $1,000-$3,000 - [Oxygen sensor replacement cost](https://diagxcar.com/cost/oxygen-sensor-replacement): $150-$450 ## Warning lights linked to this - [Check engine light](https://diagxcar.com/warning-lights/check-engine) ## Terms explained - [What is Catalytic converter?](https://diagxcar.com/glossary/catalytic-converter) --- Source page: https://diagxcar.com/codes/p0430 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.