p0420
Moderate
Cadillac · SUVs
Catalyst System Efficiency Below Threshold (Bank 1)
Quick Answer
Error code P0420 on your Cadillac 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
Likely Causes
How to Fix It
1
Verify code with diagnostic scanner
2
Test upstream and downstream oxygen sensors
3
Check for exhaust leaks
4
Replace catalytic converter if necessary
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
Oxygen sensor
Catalytic converter
Gaskets and seals
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