P0430 on GMC: How to Diagnose & Fix
Catalyst System Efficiency Below Threshold (Bank 2)
2 GMC models · 3 documented issues
P0430 on GMC by model: symptoms, diagnosis and fix
GM says sand or debris can enter the air filter box and bypass a poorly sealing air filter, damaging the oxygen sensor element and blocking the catalytic converter with sand and debris particles, which turns on the check-engine light with P0420 and/or P0430. 2014-2018 GMC Sierra with the L83 5.3L V8, L86 6.2L V8 or LV1/LV3 4.3L V6, per GM bulletin 16-NA-111 (March 2019 version).
How to Fix
Have a technician inspect the air filter housing cover, the filter seal, the sealing surface and the outlet duct for dirt bypassing the filter, as bulletin 16-NA-111 directs, before replacing any sensor or converter. The bulletin says to replace the air filter or the air cleaner assembly if it is not sealing, then repair the P0420/P0430 as needed. Normal warranty rules apply; this is not a recall or a promise of free repair.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Sources for this issue (1)
GM says sand or debris can enter the air filter box and bypass a poorly sealing air filter, damaging the oxygen sensor element and blocking the catalytic converter with sand and debris particles, which turns on the check-engine light with P0420 and/or P0430. 2014-2018 GMC Sierra with the L83 5.3L V8, L86 6.2L V8 or LV1/LV3 4.3L V6, per GM bulletin 16-NA-111 (March 2019 version).
How to Fix
Have a technician inspect the air filter housing cover, the filter seal, the sealing surface and the outlet duct for dirt bypassing the filter, as bulletin 16-NA-111 directs, before replacing any sensor or converter. The bulletin says to replace the air filter or the air cleaner assembly if it is not sealing, then repair the P0420/P0430 as needed. Normal warranty rules apply; this is not a recall or a promise of free repair.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Sources for this issue (1)
On the 3.6L V6 Canyon (LFX in 2015-2016, LGZ from 2017), the catalytic converters lose efficiency and trigger P0420 (Bank 1) and/or P0430 (Bank 2), often a downstream consequence of oil consumption, misfires or exhaust leaks that contaminate the converter substrate and O2 sensors. Both converters can fail around similar mileage since they age under identical conditions.
Common Symptoms
- Check engine light with P0420 and/or P0430
- Reduced fuel economy
- Failed emissions/smog test
- Sulfur/rotten-egg exhaust smell
How to Fix
Diagnose before replacing: rule out a faulty downstream O2 sensor or exhaust leak, and correct any oil-consumption or misfire root cause first so the new converter is not re-poisoned. Replace the affected catalytic converter(s) once root cause is addressed.
Sources for this issue (2)
P0430 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0430 mean on a GMC?
P0430 stands for "Catalyst System Efficiency Below Threshold (Bank 2)." This code means the catalytic converter on Bank 2 (the side of the engine that does not contain cylinder #1) is not reducing emissions as effectively as it should. The computer compares the readings of the oxygen sensors before and after the converter; if the downstream sensor's signal starts mirroring the upstream one, it indicates the converter is no longer storing and processing oxygen properly. This usually points to a worn-out or damaged catalytic converter, but it can also be caused by faulty sensors or upstream engine problems that have poisoned the converter. The car will generally still run, but it will fail an emissions test. On GMC it is documented across 2 models: Sierra 1500, Canyon.
What are the most common causes of P0430?
The most common causes of P0430 are: Worn-out or failed catalytic converter (Bank 2), Faulty downstream (post-cat) oxygen sensor, Faulty upstream oxygen sensor giving bad data, Exhaust leak near the converter or sensors, Engine misfire or oil/coolant burning that damaged the catalyst, Running too rich or too lean over time, Aftermarket or non-compliant catalytic converter. The specific cause varies by vehicle.
How much does it cost to fix P0430 on a GMC?
Repair costs vary widely with the root cause and GMC model; each issue on this page carries its own estimate where one is published.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.