P0430 P0xxx · Powertrain (P) Medium severity
Catalyst System Efficiency Below Threshold (Bank 2)
The bank 2 catalytic converter is no longer storing enough oxygen to smooth the exhaust — the downstream sensor is switching too much like the upstream one.
Severity guidance: Medium — drivability or emissions affected, book it in this week
Symptoms you will notice
- Failed emissions test
- Slight loss of power
- Sulphur smell
- No obvious drivability change in mild cases
Common causes
Ordered from most to least likely — start at the top.
- 1 Ageing or overheated catalyst
- 2 Exhaust leak between the two sensors
- 3 Downstream O2 sensor lazy or biased
- 4 Engine running rich or misfiring for a long period upstream
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Rule out an exhaust leak first — it is free to check and a common false cause.
- ✓ Compare upstream and downstream sensor waveforms; a healthy downstream signal is nearly flat.
- ✓ Check fuel trims and misfire counters — fix the cause before condemning the catalyst.
- ✓ Measure back-pressure to rule out a physically blocked converter.
Repair options
- Replace the catalytic converter
- Repair the exhaust leak
- Fix the upstream rich/misfire fault first
P0430 — frequently asked questions
Is the converter definitely dead? +
Not always. Fixing an exhaust leak or a rich-running fault clears maybe one in four of these codes.
Can I use a universal converter? +
You can, but on OBD-II-monitored vehicles a correctly specified converter avoids comebacks.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.