P0420 Code on Your 2024 Mitsubishi Eclipse Cross
A P0420 code on your 2024 Mitsubishi Eclipse Cross indicates the engine control module has detected reduced catalytic converter efficiency on Bank 1. The 2024 Eclipse Cross uses a 1.5L turbocharged four-cylinder engine producing 152 horsepower with a CVT transmission. As an inline four-cylinder, there is only one exhaust bank.
On a brand-new 2024 model, this code is a warranty-covered issue. Mitsubishi's excellent warranty program means you should not pay anything for the repair.
Symptoms
- Check engine light — The primary and likely only symptom
- Normal vehicle operation — No performance changes expected
- No unusual exhaust characteristics — Expected for a new-vehicle software or sensor issue
Likely Causes for the 2024 Eclipse Cross
- ECM software calibration (35% likelihood) — The engine management system may need a software update to adjust catalyst monitor thresholds.
- O2 sensor manufacturing defect (30% likelihood) — Factory sensor defects are the most common hardware cause on new vehicles.
- Exhaust assembly tolerance (20% likelihood) — Minor factory assembly variations at connections.
- Catalytic converter defect (15% likelihood) — Rare but fully warranty-covered.
What to Do
Step 1: Visit Your Mitsubishi Dealer
Schedule a warranty service appointment. All diagnosis and repairs are covered at no cost on your 2024 model.
Step 2: TSB and Software Check
Ask the dealer to check for Technical Service Bulletins and available software updates using Mitsubishi's MUT-III diagnostic system.
Step 3: Dealer Repair
The dealer will diagnose and repair the issue under warranty, whether it requires a software flash, sensor replacement, or any other fix.
Repair Costs
All free under warranty:
- Software update: $0
- O2 sensor: $0 ($130-$280 out of warranty)
- Exhaust repair: $0 ($100-$350 out of warranty)
- Catalytic converter: $0 ($800-$1,600 out of warranty)
Mitsubishi Warranty Coverage
- 5-year/60,000-mile bumper-to-bumper
- 10-year/100,000-mile powertrain
- 8-year/80,000-mile federal emissions
DIY Recommendations
Do not attempt any DIY repairs on a 2024 model under warranty. Let the Mitsubishi dealer handle everything to protect your warranty.
Prevention Tips
- Use quality gasoline — Top-tier fuel keeps the turbo engine running clean
- Follow Mitsubishi's maintenance schedule — Regular oil changes with specified oil
- Drive at highway speeds periodically — Helps maintain catalytic converter efficiency
- Respond to service notifications — Keep vehicle software up to date