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2018 Challenger R/T Check Engine Light - P0420 and P0430 Codes

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Robert C. · rep 0 · May 22, 5:39 AM · 1 replies · solved · Question

Vehicle: 2018 Dodge Challenger R/T

Hey everyone,

My 2018 Dodge Challenger R/T, with about 75,000 miles on it, just threw a Check Engine Light. I hooked up my OBD-II scanner and it's showing P0420 (Catalyst System Efficiency Below Threshold Bank 1) and P0430 (Catalyst System Efficiency Below Threshold Bank 2).

The car seems to be running okay, maybe a slight dip in fuel economy, but nothing major. No weird smells or loud exhaust noises that I can tell. I've heard these codes can be a pain.

What are the most common culprits for both banks throwing these codes simultaneously? Is there anything I can check myself before taking it to a shop? I'm hoping it's not the catalytic converters themselves, as that's a costly repair.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:39 AM

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Hello Chris,

The P0420 and P0430 codes indicate that your Challenger's catalytic converter system isn't operating at optimal efficiency for both banks. This is a common issue, and while it can point to failing catalytic converters, there are other potential causes to investigate first.

Here are the steps you can take to diagnose the problem:

  1. Check for Exhaust Leaks: Inspect your exhaust system, especially around the manifold and upstream of the catalytic converters. Leaks can introduce unmetered air, causing the O2 sensors to read incorrectly and trigger these codes.
  2. Inspect O2 Sensors: While less common for both banks to fail simultaneously, faulty upstream or downstream oxygen sensors can cause these codes. A scanner capable of live data can show you the voltage readings of your O2 sensors. Upstream sensors should fluctuate rapidly, while downstream sensors should show a relatively steady voltage, indicating the catalytic converter is working.
  3. Fuel System Check: Issues like a rich or lean fuel condition (e.g., faulty fuel injectors, a leaking fuel pressure regulator, or even a dirty air filter) can overload the catalytic converters. Check for other codes related to fuel trim or misfires.
  4. Catalytic Converter Condition: If the above checks don't reveal an issue, the catalytic converters themselves might be failing. Over time, they can become clogged or lose their efficiency. You can sometimes test their temperature difference (inlet vs. outlet) with an infrared thermometer, but this is best left to a professional.

When to See a Shop:

  • If you've performed basic visual inspections and O2 sensor live data checks and haven't found a clear culprit.
  • If you notice a significant loss of power, strong sulfur smell from the exhaust, or excessive heat from under the vehicle.
  • If the codes return immediately after clearing, especially if accompanied by other driveability issues. A professional shop can perform more advanced diagnostics, including backpressure tests and detailed O2 sensor analysis, to accurately pinpoint the problem.
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