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2018 Acura TLX P0420 Code - Catalyst System Efficiency Below Threshold

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Chris P. · rep 0 · May 25, 3:39 AM · 1 replies · solved · Question

Vehicle: 2018 Acura TLX 2.4L

Hey everyone,

My 2018 Acura TLX 2.4L just threw a Check Engine Light, and when I scanned it, I got a P0420 code. I've heard this can be a few different things, but I'm hoping it's not the catalytic converter itself.

The car seems to be running fine, no noticeable loss of power or strange smells. I recently had an oil change, but nothing else major.

Has anyone else experienced this with their TLX? What was the fix? Should I try cleaning the O2 sensors or is that a waste of time? Any advice on where to start troubleshooting would be greatly appreciated before I take it to a shop.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:39 AM

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ClearTheCode admin answer:

The P0420 code, "Catalyst System Efficiency Below Threshold (Bank 1)," indicates that your vehicle's catalytic converter is not operating as efficiently as it should be. While it often points to a failing catalytic converter, it's crucial to rule out other potential causes first.

Here's a breakdown of common causes and diagnostic steps:

  1. Oxygen Sensors: Failing upstream or downstream O2 sensors can send incorrect data to the engine control unit (ECU), leading it to believe the converter is inefficient. This is a common and often cheaper fix than replacing the converter.
  2. Exhaust Leaks: Leaks in the exhaust system before or near the catalytic converter can introduce outside air, affecting O2 sensor readings and triggering the code.
  3. Engine Misfires or Rich/Lean Conditions: Persistent engine problems like misfires, incorrect fuel mixture, or excessive oil consumption can damage the catalytic converter over time by exposing it to unburnt fuel or contaminants.
  4. Catalytic Converter Failure: Over time, catalytic converters can become clogged or internally damaged, losing their ability to efficiently convert harmful exhaust gases.

What to do:

  1. Professional Scan: While you've pulled the P0420, a professional diagnostic scan tool can provide live data from your O2 sensors, helping to determine if they are switching correctly. It can also check for other pending codes that might indicate an underlying engine issue.
  2. Visual Inspection: Check for any obvious exhaust leaks, especially around the manifold and converter.
  3. Monitor Fuel Trim: A mechanic can use a scan tool to check your long-term and short-term fuel trims. Abnormal readings can point to issues with fuel delivery or air intake.

When to see a shop:

It's highly recommended to have a qualified technician diagnose this issue. While the car may seem to run fine now, ignoring a P0420 can lead to further engine damage or significantly higher repair costs if the converter fails completely. A shop can perform a backpressure test, check O2 sensor waveforms, and accurately pinpoint the root cause, saving you time and potentially money on unnecessary parts.

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