P0430 Code: Catalyst System Efficiency Below Threshold (Bank 2)

🟠 Moderate severity · drivable

Same as P0420 but on the other cylinder bank. Drivable short-term, but the converter problem should be diagnosed soon.

What P0430 means

The downstream oxygen sensor on bank 2 shows the catalytic converter isn't cleaning exhaust efficiently. It's the bank 2 version of P0420 — same problem, opposite side of the engine.

Symptoms

Check engine light is on
Reduced fuel economy
Possible rotten-egg smell from the exhaust
Often no noticeable driving symptoms early on

Common causes

most common: Worn or failing catalytic converter (bank 2)
common: Faulty downstream oxygen sensor (bank 2, sensor 2)
common: Exhaust leak before or near the downstream sensor
less common: Engine misfire or running rich that damaged the converter
less common: Coolant or oil contamination of the converter

How to fix it

Fix	DIY?	Typical cost
Inspect for exhaust leaks and repair them before replacing anything	Yes	$50–200
Test the downstream oxygen sensor with a scan tool and replace it if faulty	Yes	$60–200
Replace the catalytic converter (bank 2)	Mechanic	$600–2500

Frequently asked questions

Is P0430 the same as P0420?

Yes — it's the same problem on the opposite cylinder bank. P0420 is bank 1 and P0430 is bank 2, which simply refers to the side of the engine containing cylinder 1 versus the other side.

Can I drive with a P0430 code?

Usually yes for a short time, but the same warning as P0420 applies: a failing converter can eventually clog and hurt performance.

How much does it cost to fix a P0430?

Typically $600–$2,500. A faulty oxygen sensor is much cheaper ($60–$200); a converter replacement is the big-ticket fix.

Related codes

P0420

P0420 Code: Catalyst System Efficiency Below Threshold (Bank 1)

P0157

P0157 Code: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

P0421

P0421 Code: Warm Up Catalyst Efficiency Below Threshold (Bank 1)

Updated 2026-08. This page is informational and not a substitute for professional diagnosis.