P0430: Catalyst System Efficiency Below Threshold Bank 2

Like P0420, but for the catalyst of bank 2, so only on V and boxer engines with one catalyst per bank; Y-pipe systems with a shared catalyst report P0420 only. The module compares the oxygen sensors before and after the bank 2 catalyst – a good catalyst smooths the rear signal. GM checks on overrun and sets the code on the first trip if the ratio falls below 0.35; Ford evaluates an index ratio or fuel integration and usually needs several trips. The monitor only runs warm, in closed loop and without misfire, fuel or sensor faults.

Low severity. Can I keep driving?Normally yes, if there is no jerking or loss of power; the immediate cost is higher emissions and the risk of failing an emissions inspection. If the light is flashing or the engine has no power, stop driving until it has been checked.

Bank 2 is the side without cylinder 1, so it only exists on V or boxer engines.

Symptoms

Check engine light on, otherwise often no change in driving
Emission test failed (higher HC, CO, NOx)
Rattling or loss of power if the catalyst has broken up

Most likely causes

Catalyst aged or poisoned (oil consumption, silicone, coolant)
Catalyst overheated by misfire or rich running
Rear oxygen sensor sluggish, dirty or unsuitable
Exhaust leak ahead of or at the rear sensor

What to check, in order

Start with the simplest. You can tick off each step.

First resolve any misfire or fuel mixture codes
Look for exhaust leaks between the engine and the second sensor
Use live data to compare the signals from both oxygen sensors
Check for a blockage by measuring exhaust back pressure
Replace the catalytic converter only at the end of the diagnosis

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P0430 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
4: Emissions
30: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0430?

Normally yes, if there is no jerking or loss of power; the immediate cost is higher emissions and the risk of failing an emissions inspection. If the light is flashing or the engine has no power, stop driving until it has been checked.

What causes code P0430?

The most common causes are: catalyst aged or poisoned (oil consumption, silicone, coolant); catalyst overheated by misfire or rich running; rear oxygen sensor sluggish, dirty or unsuitable.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.