p0420
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Chevrolet · Trucks
Catalyst System Efficiency Below Threshold Bank 1
Quick Answer
Error code P0420 on your Chevrolet Trucks 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
CK15706Colorado LT 2024Colorado Trail Boss 2024Colorado WT 2024Colorado Z71 2024Colorado ZR2 2024Silverado 1500 Custom 2024Silverado 1500 High Country 2024Silverado 1500 LT 2024Silverado 1500 LT Trail Boss 2024Silverado 1500 LTZ 2024Silverado 1500 RST 2024Silverado 1500 WT 2024Silverado 1500 ZR2 2024Silverado 2500HD High Country 2024Silverado 2500HD LT 2024Silverado 2500HD LTZ 2024Silverado 2500HD WT 2024CL14543CS10403CK10743CK10543CK20943CK30943CK10906
Likely Causes
How to Fix It
1
Verify code with a scan tool and check for related misfire codes
2
Compare upstream and downstream O2 sensor waveforms on bank 1
3
Inspect exhaust system for leaks near the catalytic converter
4
Test catalytic converter temperature differential (inlet vs. outlet)
5
Replace the 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 (bank 1)
Downstream O2 sensor (bank 1)
Exhaust gaskets
Exhaust clamps
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