P0430

P0430 Catalyst System Efficiency Below Threshold Bank 2

P0430 indicates the catalytic converter on Bank 2 is failing. UK repair costs and fixes for OBD2 fault code P0430.

UK Repair Cost
£150–£800
MOT Risk
High risk of MOT failure
Safe to Drive?
Yes but get it checked soon — a failing catalytic converter will cause an MOT failure.

What does fault code P0430 mean?

P0430 indicates the catalytic converter on Bank 2 is failing. UK repair costs and fixes for OBD2 fault code P0430. When this fault is detected, the ECU (Engine Control Unit) stores the code and illuminates the check engine light (also called the engine management light or malfunction indicator lamp) on your dashboard.

All cars sold in the UK since 1996 use the standardised OBD-II diagnostic system, meaning fault code P0430 can affect any manufacturer — including Ford, Vauxhall, BMW, Volkswagen, Toyota, Mercedes-Benz, Audi, Renault, Peugeot, Nissan, Honda, Hyundai, Kia, and all others. The code is read using an OBD-II scanner plugged into the 16-pin diagnostic port, usually located under the dashboard on the driver's side.

Symptoms of fault code P0430

These are the most common symptoms UK drivers report when this code is active:

  • Check engine light on
  • Reduced fuel economy
  • Possible sulphur smell from exhaust
  • Failed MOT emissions test

Note that some vehicles show no drivability symptoms at all — the check engine light may be the only sign. This is why scanning the fault code is essential rather than guessing at the cause.

What causes P0430?

Listed from most to least common based on UK garage data:

  1. Failing catalytic converter Bank 2
  2. Faulty downstream O2 sensor Bank 2
  3. Exhaust leak Bank 2 side
  4. Engine running rich on Bank 2

It is important to diagnose the root cause before replacing parts. Many unnecessary and expensive repairs happen because the most expensive component is replaced first without proper testing. Always work through the diagnostic steps systematically.

How to fix P0430 — step by step

Work through these steps in order to avoid unnecessary parts replacement:

  1. Check for related codes — fix misfires or fuel trim codes first
  2. Test downstream O2 sensor Bank 2 with live data
  3. Inspect Bank 2 exhaust for leaks
  4. Replace catalytic converter if sensors test fine

After any repair, clear the fault code with an OBD-II scanner and carry out a test drive. If the code returns, continue to the next diagnostic step. For a personalised repair guide specific to your vehicle's make, model, year and engine, use our AI Diagnostic Report below.

UK vehicles commonly affected by P0430

These models are frequently seen with this fault code in UK garages:

  • BMW 3/5/6/7 Series (V6/V8)
  • Volkswagen Passat V6
  • Audi A4/A6 (V6)
  • Ford Mondeo/S-Max (V6)
  • Mercedes C/E Class (V6)

This code can appear on any OBD-II vehicle (all UK cars since 1996) but is more common on the models listed above. If your vehicle is not listed, it does not mean the code cannot affect it — it simply means these models are statistically more frequent in UK repair data.

DIY difficulty and cost guide

Difficulty: Medium to hard — V6/V8 exhaust work is more complex than inline 4-cylinder.

UK repair cost estimate: £150–£800 including parts and labour at average UK workshop rates (inc. VAT). Independent garages are typically 30–50% cheaper than main dealers. Always get at least two quotes.

Prevention: Regular servicing, fix misfires promptly, quality fuel.

P0430 and the UK MOT test

Fault code P0430 is likely to cause an MOT failure. Under current DVSA testing standards, an illuminated malfunction indicator lamp (MIL / check engine light) is an automatic MOT failure, regardless of whether the vehicle is otherwise roadworthy. This means you must resolve this fault before your MOT test.

Even if the light is not currently on, if the fault is intermittent it could reappear during the test. Use our AI Diagnostic Report to understand the MOT risk specific to your vehicle and get advice on whether it is safe to proceed to your test.

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Frequently asked questions about P0430

Can I drive with fault code P0430?

Yes but get it checked soon — a failing catalytic converter will cause an MOT failure.

Will P0430 clear itself?

Some fault codes will clear automatically after the underlying issue resolves itself, but P0430 typically stays stored until the fault is fixed and the code is manually cleared with an OBD-II scanner. Do not assume the problem has gone away if the light turns off temporarily.

Do I need a garage or can I fix P0430 myself?

Medium to hard — V6/V8 exhaust work is more complex than inline 4-cylinder.

How much does it cost to fix P0430 in the UK?

UK repair costs for P0430 typically range from £150 to £800 depending on your vehicle, the root cause, and your local garage rates. Use our AI Diagnostic Report for a cost estimate specific to your car.

Related OBD2 fault codes

These fault codes are commonly found alongside P0430 or share similar causes:

P0420
Catalyst System Efficiency Below Threshold Ba…
P0174
System Too Lean Bank 2
P0300
Random/Multiple Cylinder Misfire Detected
P0136
O2 Sensor Circuit Malfunction Bank 1 Sensor 2
P0161
O2 Sensor Heater Circuit Malfunction Bank 2 S…

Last updated: May 2026. AI-Diagnostics-Pro provides AI-generated information for educational purposes only. It is not a substitute for professional automotive advice. Always consult a qualified mechanic before carrying out vehicle repairs. Repair cost estimates are approximate and may vary by region and vehicle.