What Does P0420 Mean on a 2020 Dodge Challenger?
A P0420 trouble code on your 2020 Dodge Challenger means the engine control module has detected that the catalytic converter on Bank 1 is not converting exhaust gases as efficiently as expected. The 2020 Challenger comes with several engine choices: the 3.6L Pentastar V6 (305 hp) in the SXT, the 5.7L HEMI V8 (375 hp) in the R/T, the 6.4L HEMI V8 (485 hp) in the Scat Pack, and the supercharged 6.2L HEMI (717+ hp) in the Hellcat variants. All of these engines use catalytic converters, and any of them can trigger a P0420.
Don't assume the worst right away. While a bad catalytic converter is a possibility, there are other issues that can cause this exact same code for a fraction of the repair cost.
Symptoms to Look For
- Check engine light on — The primary and sometimes only indicator
- Reduced fuel economy — You may notice more frequent fill-ups
- Rotten egg smell — A sulfur odor from the exhaust suggests converter trouble
- Mild hesitation — Some owners report slight performance changes
- Failed state emissions test — The code causes an automatic failure
Top Causes of P0420 on the 2020 Challenger
1. Aging Catalytic Converter
With the 2020 Challenger now having several years on the road, the catalytic converter may be reaching the end of its effective life, particularly on higher-mileage examples. The HEMI engines produce significant heat, which can accelerate converter wear. The internal precious metal coating gradually degrades, reducing its ability to process harmful emissions.
2. Bad Downstream O2 Sensor
The Bank 1 downstream oxygen sensor is the detector that actually triggers this code. If the sensor itself has failed or become contaminated with oil or carbon, it may report false readings. On the Challenger, this sensor is positioned after the catalytic converter and is accessible from underneath the vehicle.
3. Exhaust Leak
Exhaust leaks between the engine and the downstream O2 sensor can introduce ambient air into the exhaust stream. This extra oxygen tricks the sensor into thinking the converter isn't doing its job. The Challenger's exhaust manifold bolts and gaskets are common leak points, especially after heat cycling over several years.
4. Engine Running Rich
If the engine is consistently running rich due to a faulty upstream O2 sensor, stuck-open injector, or fuel pressure issue, the excess fuel can overwhelm the catalytic converter. Over time, this damages the catalyst material and reduces its efficiency permanently.
How to Diagnose P0420
- Scan for all codes — Check for accompanying codes that provide additional context. Misfire codes or O2 sensor codes alongside P0420 change the diagnostic approach.
- Monitor O2 sensor live data — Watch the upstream and downstream O2 sensors on Bank 1. A healthy converter shows the downstream sensor with a relatively steady voltage compared to the rapidly switching upstream sensor.
- Inspect the exhaust visually — Look for rust, holes, loose connections, and damaged gaskets from the manifold to the converter area.
- Perform a backpressure test — Excessive backpressure can indicate a clogged or collapsed converter substrate.
Repair Costs for 2020 Challenger
- Catalytic converter replacement: $1,000 – $2,800 depending on engine. The V8 models are more expensive due to larger converters.
- Downstream O2 sensor: $120 – $300 for parts and labor
- Exhaust leak repair: $100 – $450 depending on location and extent
- Engine running rich repair: $150 – $550 covering injectors, sensors, or fuel system components
Can You Drive With P0420?
Yes, your 2020 Challenger is safe to drive with a P0420 code in the short term. The code itself doesn't indicate any dangerous condition. However, if you notice performance changes, unusual smells, or additional warning lights, get it checked sooner rather than later. A clogged converter can eventually cause serious engine problems.
Prevention Tips
- Fix misfires right away — Unburned fuel is the fastest way to kill a catalytic converter
- Use the correct fuel grade — HEMI engines are designed for premium fuel
- Maintain your ignition system — Replace spark plugs at the recommended intervals
- Avoid aftermarket tune complications — Modified Challengers with aggressive tunes can stress the converter