Powertrain, generic · Auxiliary emission controls
P0430 Catalyst System Efficiency Below Threshold Bank 2
Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo
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.
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
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
Repair estimate
DifficultyMediumDIY possible
Parts and labour€80–1,800
Time0.5–3 h
Typical range across vehicles; the real cost depends on what the testing finds.
What to check first
- Check for exhaust leaks
- Compare O2 signals
- Rule out misfire and rich running
Parts involved
catalytic converterdownstream oxygen sensorupstream oxygen sensorengine control module
Related codes
References: law.cornell.edu, gsi.ext.gm.com, fordservicecontent.com, newtonnet.co.uk.