HomeBrandsBMWSUVsp0420
p0420
Call a Pro
BMW · SUVs
Catalyst System Efficiency Below Threshold Bank 1
Quick Answer
Error code P0420 on your BMW SUVs means: Catalyst System Efficiency Below Threshold Bank 1. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
X1 M35i 2024X1 xDrive28i 2024X3 M 2024X3 M40i 2024X3 xDrive30i 2024X5 M 2024X5 M60i 2024X5 xDrive40i 2024X5 xDrive50e 2024X6 M 2024X6 M60i 2024X6 xDrive40i 2024X7 M60i 2024X7 xDrive40i 2024iX M60 2024iX xDrive50 2024X1X3 MX3X5 MX5X6X7iX
Likely Causes
  1. Deteriorated or contaminated catalytic converter
  2. Faulty downstream oxygen sensor
  3. Exhaust leak at the manifold or catalytic converter
  4. Long-term engine misfire causing catalyst damage
  5. Oil consumption contaminating the catalyst substrate
How to Fix It
1
Ensure no other engine codes are present that could harm the catalyst
2
Compare upstream and downstream O2 sensor waveforms with a scan tool
3
Inspect exhaust system for leaks at all connections
4
Measure catalytic converter inlet and outlet temperatures
5
Replace catalytic converter if efficiency is confirmed below threshold
Pro Tip
This issue typically requires professional diagnosis. Attempting this fix without proper training could cause further problems.
Parts You May Need
Catalytic converter
Downstream oxygen sensor
Exhaust gaskets
Exhaust clamps
Related Error Codes
P0171P0174P0300P0301P0335
Video Guides
Loading video guides…
Search more on YouTube →