BMW Emissions / Cat Fault Codes
Catalyst efficiency, EVAP leaks, post-cat O2 sensor faults.
4 codes in this category.
P0420Catalyst Efficiency Below Threshold (Bank 1)Pre-cat O2 sensor and post-cat O2 sensor reading too similar - cat is wearing.moderateP0430Catalyst Efficiency Below Threshold (Bank 2)Same as P0420 but on the second bank (V8/V10/V12 BMWs).moderateP0455EVAP Large Leak DetectedLarge evaporative emissions leak - check gas cap first.lowP0456EVAP Small Leak DetectedSmall evap leak - usually cracked hose or aging purge valve.low