P0422: Catalyst 2 Efficiency Below Threshold Bank 1
What to do
Driveable, will fail an emissions test. Tapping the converter body and listening for a rattle costs nothing and sometimes settles the question immediately.
What this code means
The main under-floor converter on bank 1 is not meeting its efficiency threshold. On systems that carry both a close-coupled warm-up converter and a larger main one, this code distinguishes the second from the first — useful, because it narrows which part of the exhaust to inspect and which sensor pair the module was comparing.
The main converter sits further from the engine and runs cooler, so it tends to fail through gradual age and contamination rather than the sudden thermal damage that kills warm-up units. Substrate that has broken up will also rattle when the case is tapped, which is a genuine and free diagnostic.
Likely causes
Start here
- Failed catalytic converter · specialist
- Aged or lazy downstream oxygen sensor · easy
- Exhaust leak before the sensor · moderate
Less common
- Broken or collapsed converter substrate · specialist
- Converter poisoned by oil or coolant consumption · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0422.