BMW 3-Series · Diagnostic Trouble Code
P0420 — Catalyst System Efficiency Below Threshold (Bank 1)
Quick overview of P0420 on your BMW 3-Series. Read the full diagnosis guide, then find the repair guides for your vehicle below.
Repair guides that fix P0420
General diagnostic information, not a factory service procedure. If you're unsure, have a qualified technician confirm the diagnosis before buying parts.