The Quick Answer above is the generic definition. What follows is what is documented for the BMW models that log P0422, checked against manufacturer data and owner reports.
DTC/P0422·BMW
P0422 on BMW: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)BMW
P0422 on a BMW means the main catalytic converter on Bank 1 has dropped below the efficiency threshold the ECU expects. It is similar to P0420 but used on some manufacturers (notably Chrysler, Jeep, and certain European platforms) to distinguish the main cat from the upstream warm-up cat in multi-brick exhaust systems.
Repair cost on BMW€105 - €1660
Connect any standard Bluetooth OBD2 adapter to your BMW and Skanyx tells you what P0422 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
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BMW 3 Series
2006-2024P0422 on BMW 3 Series with N52, N55, or B58 inline-6 engines typically points to the main underfloor cat rather than the manifold-mounted pre-cat. On these engines, the main cat is a separate unit that is easier and cheaper to replace than the integrated pre-cat. Check for VANOS rich-running history because long-term overfuelling will kill the main cat well before 200,000 km.
What causes P0422 on a BMW?
Beyond the generic causes listed on the main P0422 page, these are the documented BMW-specific patterns:
BMW 3 SeriesUnderfloor main cat degradation, often after VANOS-related rich running
BMW 3 SeriesFailing fuel injector causing intermittent enrichment on Bank 1
How to diagnose P0422 on a BMW with OBD2
Follow these steps to pinpoint the root cause of P0422:
- Read freeze frame data and check for companion catalyst codes (P0420, P0421) that may be active at the same time
- Inspect the full Bank 1 exhaust run for leaks, especially at flange joints and slip-fit connectors after the main cat
- Graph the Bank 1 downstream O2 sensor at steady 2,000 to 2,500 RPM. A healthy main cat keeps it stable around 0.4 to 0.6 V
- If the downstream signal swings more than 0.2 V repeatedly, the main cat is no longer storing oxygen and is failing
- Test downstream sensor switching speed. Anything over 300 ms is sluggish and may be the actual fault
How much does P0422 cost to fix on a BMW? (EUR)
Estimated repair costs for P0422 in EUR, compiled across makes. Expect BMW parts and labour towards the upper end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0422 on BMW
These codes commonly cluster with P0422 on BMW vehicles:
Looking for the full P0422 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0422 guideSkanyx · BMW
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