What it means
P0420 — Catalyst system efficiency below threshold (Bank 1). BeeEmUu groups this code under Powertrain with a severity of Service soon.
P0420Provenance
The title and severity above are seeded from the open-research source of record: https://www.sae.org/standards/content/j2012_202104/. BeeEmUu stores short factual descriptions only; no proprietary ISTA or OEM text is reproduced.
Related schematics
No schematic cross-link is seeded for this code yet. The schematic library holds the CC0 seed diagrams; community links are added over time.
Community repair opinions
No community opinion file exists for this code yet. Add one by opening a PR with community/opinions/P0420.toml.
Frequently asked
Is code P0420 safe to clear?
Clearing is only safe once you have read and recorded the freeze frame. Re-appearing after a clear is the useful signal; clearing without recording destroys it.
Is P0420 a BMW-specific or a generic code?
This is a generic SAE J2012 code, so any OBD-II tool can read it.