p0420
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Volkswagen · SUVs
Catalyst System Efficiency Below Threshold Bank 1
Quick Answer
Error code P0420 on your Volkswagen 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
CAID4ID6B25N5N-LWBCRAtlas Cross Sport SE 2024Atlas Cross Sport SEL 2024Atlas Cross Sport SEL R-Line 2024Atlas SE 2024Atlas SEL 2024Atlas SEL Premium R-Line 2024ID.4 Pro 2024ID.4 Pro S 2024ID.4 Pro S Plus 2024ID.4 Standard 2024Taos S 2024Taos SE 2024Taos SEL 2024Tiguan S 2024Tiguan SE 2024Tiguan SEL 2024Tiguan SEL R-Line 2024
Likely Causes
How to Fix It
1
Check for and address any other DTCs that could cause catalyst damage before replacing the converter
2
Monitor upstream and downstream O2 sensor waveforms with a scan tool; the downstream signal should be nearly flat
3
Inspect the exhaust system for leaks at the exhaust manifold, downpipe flanges, and flex pipe
4
Measure the temperature differential across the catalytic converter to assess internal efficiency
5
Replace the catalytic converter with an OEM or CARB-compliant unit if confirmed failed
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 O2 sensor
Exhaust gaskets and hardware
Flex pipe (if damaged)
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