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2018 Charger R/T Check Engine Light - P0420 Code

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Chris P. · rep 0 · May 22, 5:37 AM · 1 replies · solved · Question

Vehicle: 2018 Dodge Charger R/T

Hey everyone,

My 2018 Dodge Charger R/T, with about 75,000 miles on it, just threw a Check Engine Light this morning. I hooked up my OBD-II scanner, and it's showing a P0420 code: 'Catalyst System Efficiency Below Threshold (Bank 1)'.

The car seems to be running fine, no noticeable loss of power, no strange smells, and fuel economy seems normal. I haven't heard any rattling from underneath either, which I know can sometimes indicate a failing catalytic converter.

I'm hoping it's not the catalytic converter itself, as those can be pretty expensive. Has anyone else experienced this specific code on their Charger or other Dodge models? What were the common culprits you found? Any advice on where to start troubleshooting before I take it to a shop?

Thanks in advance for any help!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:37 AM

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ClearTheCode admin answer:

The P0420 code on your 2018 Dodge Charger R/T indicates that the catalytic converter on Bank 1 (the side of the engine with cylinder #1) is not operating at optimal efficiency. While it often points to a failing catalytic converter, there are several other potential causes that are worth investigating first.

Here are the common causes and troubleshooting steps:

  1. Exhaust Leaks: Even small leaks in the exhaust system before or near the catalytic converter can cause the oxygen sensors to read incorrectly, triggering a P0420. Inspect the exhaust manifold, gaskets, and pipes for any signs of leaks (soot marks, hissing sounds).
  2. Faulty Oxygen Sensors: The P0420 code relies on readings from both the upstream (pre-cat) and downstream (post-cat) oxygen sensors. A failing downstream O2 sensor, or even an upstream one providing inaccurate data, can falsely trigger this code. You can monitor O2 sensor readings with a good scan tool to check their activity.
  3. Engine Misfires or Rich/Lean Conditions: Persistent engine misfires, running too rich (too much fuel) or too lean (not enough fuel) can damage the catalytic converter over time or cause it to operate inefficiently. Check for other pending or active codes related to misfires (P030x) or fuel trim issues.
  4. Contaminated Fuel or Additives: Using poor quality fuel or certain fuel additives can sometimes affect converter efficiency. Ensure you're using the recommended fuel type for your Charger.
  5. Failing Catalytic Converter: If all other potential causes are ruled out, the catalytic converter itself is likely failing. This can be due to age, internal damage, or contamination.

When to See a Shop:

  • If you've checked for exhaust leaks and O2 sensor issues (if you have the tools) and found nothing conclusive.
  • If you notice any performance issues like reduced power, poor fuel economy, or a sulfur smell.
  • If the Check Engine Light is flashing, which indicates a severe misfire that could rapidly damage the catalytic converter.
  • If you're uncomfortable performing diagnostic steps yourself, a professional technician can perform a comprehensive diagnosis, including backpressure tests and advanced O2 sensor analysis, to pinpoint the exact cause of the P0420 code.
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