p0420
Moderate
Buick · SUVs
Catalyst System Efficiency Below Threshold (Bank 1)
Quick Answer
Error code P0420 on your Buick SUVs means: Catalyst System Efficiency Below Threshold (Bank 1). This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Verify with OBD-II scanner and check live data
2
Inspect exhaust system for leaks or damage
3
Test pre and post-catalyst oxygen sensors
4
Measure exhaust backpressure
5
Replace catalytic converter if faulty
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Catalytic converter
Oxygen sensors
Exhaust clamps
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