OBD-II trouble code
P0430: Catalyst System Efficiency Below Threshold (Bank 2)
The engine computer detected that the catalytic converter on Bank 2 is not reducing emissions as efficiently as expected. Same condition as P0420, but for the opposite side of a V-configured engine. The check engine light is on, but the car is usually still drivable.
Quick facts
- System
- Powertrain
- Category
- Emissions / Catalyst
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $200 – $2,500
- DIY difficulty
- Intermediate DIY
What does P0430 mean?
P0430 is the Bank 2 equivalent of P0420. The engine control module (ECM) monitors catalyst efficiency by comparing oxygen sensor readings before and after the catalytic converter. A healthy catalyst smooths the post-cat oxygen signal compared to the pre-cat signal. When the two signals look too similar over time, the ECM concludes the catalyst has lost efficiency and sets P0430.
Bank 2 refers to the side of the engine that does not contain cylinder number 1. P0430 only applies to V-configuration engines (V6, V8, etc.) and a small number of horizontally-opposed and inline configurations that use two catalytic converters. On inline engines with one bank, P0420 is the only catalyst code that applies.
It's not unusual to see P0420 and P0430 set together on aging V-engines, since both catalytic converters age at similar rates. The same diagnostic logic applies to both — address misfire codes, oxygen sensor problems, and exhaust leaks before assuming the catalyst itself is bad.
Common causes
- Failing or worn catalytic converter on Bank 2 (the most common cause after high mileage)
- Downstream Bank 2 oxygen sensor degraded or slow to respond
- Exhaust leak upstream of the Bank 2 catalytic converter
- Engine misfire on a Bank 2 cylinder damaging the catalyst
- Contaminated fuel or oil burning past the rings, fouling the catalyst
- Aftermarket high-flow catalytic converter that doesn't meet OEM efficiency
- Faulty engine coolant temperature sensor causing rich running
Symptoms
- Check engine light is on
- Vehicle will fail an OBD-II emissions test
- Slight reduction in fuel economy in some cases
- Often no driveability symptoms at all
Diagnostic steps
- 1.Scan the vehicle for other codes. Address misfire codes (P0300-series), lean conditions (P0174 for Bank 2), and oxygen sensor codes before assuming the catalyst is bad.
- 2.Inspect the exhaust system on the Bank 2 side for leaks upstream of the catalytic converter, including the manifold and gaskets.
- 3.Compare voltage waveforms from the upstream and downstream Bank 2 oxygen sensors with a scan tool. A downstream sensor switching as quickly as the upstream is a strong sign of catalyst failure.
- 4.Test the downstream Bank 2 oxygen sensor against the manufacturer's specification. A slow or lazy sensor can cause P0430 even with a healthy catalyst.
- 5.If everything else checks out, the Bank 2 catalytic converter is the likely failure.
Repair cost
$200 – $2,500
Range is wide because the fix could be as simple as a $200 oxygen sensor replacement or as expensive as a $1,500-$2,500 OEM catalytic converter on a luxury or hybrid vehicle. Aftermarket cats run $300 to $800 installed on most mainstream vehicles. If P0420 is also set, expect to repair both catalysts at once.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with catalytic converter replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.