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2018 TLX Check Engine Light - P0420 Code

0

Angela R. · rep 0 · May 22, 4:53 AM · 1 replies · solved · Question

My 2018 Acura TLX A-Spec, with about 85,000 miles, just threw a Check Engine Light. I used my OBD-II scanner and it's showing a P0420 code: "Catalyst System Efficiency Below Threshold (Bank 1)". The car seems to be driving fine, with no noticeable loss of power or strange noises.

I'm wondering if this is something I can troubleshoot myself or if it's definitely a trip to the dealer. I've heard sometimes it can be an O2 sensor, but I'm not sure how to confirm that.

Are there any common causes for this code on these Acura TLX models? Any advice on where to start looking would be greatly appreciated.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:53 AM

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ClearTheCode guidance (Acura · Diagnostics & codes)

Summary: For 2018 TLX Check Engine Light - P0420 Code, work through these steps on your 2016+ vehicle:

  1. Confirm the symptom — note when it happens (cold start, highway, after fuel fill, etc.).
  2. Scan codes — save all pending/stored DTCs; don't clear until you've recorded them.
  3. Check TSBs & recalls — look up your VIN for open campaigns and known fixes.
  4. Inspect the obvious — related fuses, connectors, fluid level, and recent repairs.
  5. Test the common fix — follow model-specific service procedures; one change at a time.
  6. Escalate if needed — burning smell, no brakes, overheating, or stalling in traffic → shop visit.

Owner reported: My 2018 Acura TLX A-Spec, with about 85,000 miles, just threw a Check Engine Light. I used my OBD-II scanner and it's showing a P0420 code: "Catalyst System Efficiency Below Threshold (Bank 1)". The car seems to be driving fine, with no noticeable loss of power or strange noises.

I'm wondering if this is something I can troubleshoot myself or if it's definitely a trip to the dealer. I've heard so…

This is educational guidance, not a substitute for hands-on diagnosis.

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