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2020 Aviator Grand Touring: P0420/P0430 Codes & Poor MPG

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Mike T. · rep 0 · May 25, 4:28 AM · 1 replies · solved · Question

Vehicle: 2020 Lincoln Aviator Grand Touring

Hey forum,

I'm driving a 2020 Lincoln Aviator Grand Touring, and the check engine light came on recently. When I scanned it, I got codes P0420 and P0430, which are both related to catalytic converter efficiency (Bank 1 and Bank 2, respectively). On top of that, my fuel economy seems to have taken a hit. I'm not getting the MPG I used to.

The car feels a bit sluggish sometimes, but no major driveability issues yet. Could both catalytic converters really be failing at the same time, or is there an underlying issue causing this? What should I be looking at first?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:28 AM

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ClearTheCode admin answer:

Receiving both P0420 and P0430 codes simultaneously, along with reduced fuel economy, indicates a problem affecting both banks of your engine's exhaust system, or a systemic issue causing the converters to fail prematurely. It's less likely for both converters to fail at the exact same time without an underlying cause. Here's a breakdown:

  1. Oxygen Sensors (O2 Sensors): Faulty upstream or downstream O2 sensors can provide incorrect readings to the engine control unit (ECU), leading it to believe the catalytic converters are inefficient. If both downstream sensors are failing, it could trigger both codes. Upstream sensors, if inaccurate, can cause the engine to run rich or lean, which can damage the converters over time.

  2. Exhaust Leaks: Leaks in the exhaust system before the downstream O2 sensors can allow ambient air in, skewing sensor readings and falsely indicating converter inefficiency.

  3. Engine Running Rich/Lean: An underlying engine problem causing the air-fuel mixture to be consistently too rich (too much fuel) or too lean (too much air) can overheat and damage catalytic converters. Common causes include:

    • Failing Fuel Injectors: Leaky or stuck-open injectors can cause a rich condition.
    • Mass Air Flow (MAF) Sensor: An inaccurate MAF sensor can lead to incorrect fuel calculations.
    • Engine Coolant Temperature (ECT) Sensor: A faulty ECT sensor can cause the engine to run rich if it thinks the engine is always cold.

  4. Catalytic Converter Failure: While less likely for both simultaneously, internal damage or clogging of the converters can occur due to age, extreme heat, or exposure to unburnt fuel/oil. This would directly cause the codes.

OBD Codes:

  • P0420: Catalyst System Efficiency Below Threshold (Bank 1)
  • P0430: Catalyst System Efficiency Below Threshold (Bank 2)

When to See a Shop:

  • Promptly: While not immediately critical, continued driving with these codes can lead to further damage to the catalytic converters, which are expensive to replace. The reduced fuel economy also means you're wasting gas.
  • A professional can perform comprehensive diagnostics, including checking O2 sensor readings, fuel trim values, and backpressure tests to determine the root cause before recommending converter replacement.
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