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Check Engine Light P0420 on 2019 QX80

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Heather Y. · rep 0 · May 22, 5:02 AM · 1 replies · solved · Question

Vehicle: 2019 Infiniti QX80 Luxe

Hey everyone,

My 2019 Infiniti QX80 Luxe just threw a check engine light. I scanned it with my OBD-II reader, and the only code that came up is P0420. It says 'Catalyst System Efficiency Below Threshold (Bank 1)'.

The car seems to be driving fine, no noticeable loss of power, no strange noises, and fuel economy seems normal. I just filled up with gas a couple of days ago, but it was from my usual station. Could this be something simple, or am I looking at a costly catalytic converter replacement?

Any advice on what to check first would be great!

Thanks!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:02 AM

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ClearTheCode admin answer:

The P0420 code on your 2019 Infiniti QX80 indicates that the catalytic converter on Bank 1 (the side of the engine with cylinder #1) is not operating at optimal efficiency. While it can point to a failing catalytic converter, it's important to rule out other, less expensive causes first.

Here are the common causes and diagnostic steps:

  1. Oxygen Sensors (O2 Sensors): The P0420 code is often triggered by the downstream (post-catalytic converter) O2 sensor. If this sensor is faulty, it might incorrectly report that the catalyst is inefficient. The upstream O2 sensor can also contribute if it's providing incorrect fuel mixture data.
  2. Exhaust Leaks: Any leak in the exhaust system before or between the O2 sensors on Bank 1 can allow unmetered air in, skewing sensor readings and triggering a P0420. Listen for hissing or puffing sounds from the exhaust.
  3. Engine Misfires or Rich/Lean Conditions: Persistent engine misfires (P030x codes) or an engine running consistently too rich or too lean can overload the catalytic converter, causing it to fail prematurely or trigger the efficiency code. Ensure there are no other active engine codes.
  4. Contaminated Fuel/Oil: Certain fuel additives, leaded fuel (unlikely in modern vehicles), or excessive oil burning can contaminate and damage the catalytic converter over time.
  5. Failing Catalytic Converter: If all other possibilities are ruled out, the catalytic converter itself may have degraded and is no longer effectively converting harmful emissions.

When to see a shop:

While your QX80 might seem to drive normally, a P0420 code means your vehicle is likely emitting more pollutants than allowed, and ignoring it can lead to further issues or failing emissions tests. If you're not comfortable inspecting exhaust components or testing O2 sensors, it's best to take your vehicle to a trusted mechanic. They can perform a smoke test for exhaust leaks, monitor O2 sensor data with a professional scan tool, and perform backpressure tests to accurately diagnose whether the catalytic converter truly needs replacement or if a simpler fix is possible.

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