P0422 on BMW: Causes, Symptoms and Fix Cost
Quick Answer
Safe to drive (short-term)
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.
- Severity
- Moderate · Emissions
- Typical repair cost, all makes
- €105-€1660
Connect a standard OBD2 adapter (Bluetooth LE on iPhone) 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.
Get Skanyx freeWhat does P0422 mean on a BMW?
The Quick Answer above is the generic definition. What follows is the model-specific detail for the BMW models that log P0422.
BMW 3 Series
2006-2024
On the N52 the close-coupled converters are built into the exhaust manifolds, while on the turbocharged N55 and B58 the close-coupled converter sits directly after the turbocharger rather than on the manifold. Any further underfloor converter is a separate bolt-in unit that is easier and cheaper to replace than the close-coupled one. Check for VANOS or fuel-trim rich-running history, because long-term overfuelling kills a catalyst early.
What causes P0422 on a BMW?
Beyond the generic causes listed on the main P0422 page, these are the patterns noted for BMW models:
Underfloor main cat degradation, often after VANOS-related rich running
: BMW 3 Series
Failing fuel injector causing intermittent enrichment on Bank 1
: BMW 3 Series
How to diagnose P0422 on a BMW with OBD2
- 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.
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Replace main catalytic converter (Bank 1) | €220–€1400 | €90–€260 | €310–€1660 | Professional |
| Replace downstream O2 sensor (Bank 1) | €55–€160 | €60–€130 | €115–€290 | Moderate |
| Fix exhaust leak (gasket or pipe section) | €25–€120 | €80–€220 | €105–€340 | Moderate |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
Codes related to P0422
These codes are often seen alongside P0422 or point to related issues, on any make:
Looking for the full P0422 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0422 guide