What is the difference between P0420 and P0430?

Both codes mean low catalytic converter efficiency. P0420 refers to bank 1 and P0430 to bank 2, which only V and boxer engines with two catalytic converters have.

Can I drive with code P0430?

Usually yes, if the light stays on steadily and the engine runs normally. If the light flashes or the engine runs badly, stop driving and have the car checked.

Will my car pass its MOT with code P0430?

In the UK, an engine management light that shows a fault is a major defect, so the car fails its MOT. This applies to most petrol cars first used from 1 July 2003. Elsewhere in Europe it depends on your country’s inspection rules; the EU roadworthiness directive lists an OBD read-out showing a significant malfunction as a reason for failure on petrol cars. This fault also affects exhaust emissions, so the car may fail the emissions test as well. It is safer to have it fixed before the test.

P0430: Catalyst Efficiency Below Threshold (Bank 2)

When the code is set

The ECM compares the signals from the oxygen sensors before and after the catalytic converter on the bank 2 side of the engine. When the rear sensor starts switching as quickly as the front one, the converter is no longer storing enough oxygen, so the ECM stores the code. If P0420 is also stored, either both converters are affected or there is a shared cause, such as an engine running problem.

Can I keep driving?

Usually safe to drive

A car with a weak catalytic converter usually runs normally, so you can normally keep driving and mention the code at your next service. If the check engine light flashes, the engine runs unevenly or something rattles under the car, stop when it is safe and speak to a mechanic.

Symptoms

The check engine light is on, often with no other symptoms.
A rotten-egg (sulphur) smell from the exhaust.
Rattling under the car if the inside of the converter has broken up.
Rough idle or stalling if the converter is blocked.
High readings in an exhaust emissions test.

Common causes

A worn or damaged catalytic converter on the bank 2 side – the most common cause.
A faulty rear oxygen sensor or its wiring.
An exhaust leak ahead of the converter.
Leaking injectors or misfires in the bank 2 cylinders.
Outdated engine control module software (on some models).

How to find the cause

A mechanic usually works like this:

Read all stored codes and freeze frame data, and check whether P0420 is stored too.
Check for exhaust leaks ahead of the converter.
Inspect both bank 2 oxygen sensors and their wiring, and compare their signals on a test drive.
Fix any misfires or leaking injectors before replacing the converter.
After the repair, clear the code and confirm on a test drive that the catalyst test passes.

Notes by make

Audi: In the US, Audi issued a service bulletin for codes P042000 and P043000 on some models with the 3.0 TFSI engine (2011–2015 S4 and S5, 2012–2014 A6, A7 and A8, and 2013–2015 Q5): the cause was the engine control module software and the fix was a software update. A workshop can check whether this applies to your car.

Other ways the code is written

Scan tools and workshop printouts sometimes show the code with extra characters:

P043000

Related codes

Frequently asked questions

Evoca fault code diagnostics is an informational aid and does not replace a professional inspection of your vehicle. Only an inspection of the vehicle at a workshop can confirm the cause of a fault.

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P0430 code: catalytic converter efficiency below threshold (bank 2)