P0420 on BMW
Diagnostic trouble code · BMW · Bank 1
BMW · 5 Series · F10 · 2010–2017 · Sedan / Touring
- N20
- N55
- N47
- N57
What P0420 means
P0420 means the catalytic converter on Bank 1 is operating below its efficiency threshold. On BMW it commonly points to an ageing catalyst or an upstream/downstream oxygen-sensor discrepancy rather than an immediate failure. Does not affect driving safety directly.
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General information, not a diagnosis or repair instruction. Always confirm with a qualified mechanic for your specific vehicle.
Common causes
- Natural catalyst wear
- Aged or failing catalytic converter
- Faulty rear oxygen sensor
- Faulty upstream oxygen sensor
- Exhaust leak or burn-through
Symptoms
- Повышенный расход топлива
- Sulfur smell from the exhaust
What to check first
- Read live O2-sensor data — compare upstream vs downstream switching
- Inspect the exhaust for leaks around the catalytic converter
- Check for pending misfire or fuel-trim codes first
- Confirm the catalyst with a professional back-pressure / efficiency test before replacing
| Estimated repair cost range | USD |
|---|---|
| Low | $600.00 |
| Typical | $1,400.00 |
| High | $2,800.00 |
Based on an official source
Frequently asked questions
Can I drive with P0420 on my BMW?
Usually yes in the short term — P0420 does not typically affect immediate drivability or safety. However, it will not clear on its own and can lead to a failed emissions test, so have it diagnosed rather than ignored.
Is it always the catalytic converter?
No. On BMW F10, P0420 is frequently caused by a failing downstream oxygen sensor or an exhaust leak, both far cheaper than a catalytic converter. Rule those out with live O2 data before replacing the catalyst.
How much does it cost to fix P0420 on an F10?
It depends on the root cause: an oxygen sensor is a lower-cost repair, while a genuine catalytic-converter replacement is the upper end of the range. Get the cause confirmed before authorising a catalyst replacement.