What Does Code P0420 Mean on a 2024 Subaru Crosstrek?
If your 2024 Subaru Crosstrek is showing a P0420 code, the ECU has determined that the Bank 1 catalytic converter is not efficiently processing exhaust gases. The 2024 Crosstrek features a 2.5L FA25 horizontally-opposed boxer-4 engine producing 182 horsepower and 178 lb-ft of torque. A 2.0L hybrid option is also available. Both use the Lineartronic CVT and Symmetrical AWD.
On a new 2024 model, P0420 is uncommon and typically indicates a manufacturing or software issue that falls under warranty coverage.
Common Symptoms
- Check engine light on
- Slight fuel economy reduction from the rated 28 city/34 highway MPG
- Possible faint sulfur smell
- Emissions test failure
- No significant drivability issues
Most Likely Causes on the 2024 Crosstrek
1. ECU Software Calibration
The most likely cause on a new Crosstrek is a software calibration issue. Subaru regularly issues ECU updates that fine-tune catalyst monitoring algorithms for the FA25 engine.
2. Faulty Downstream O2 Sensor
A manufacturing defect in the rear oxygen sensor can produce false readings. The Crosstrek's higher ground clearance means the sensor is more exposed to off-road debris and water, which can contribute to issues.
3. Exhaust System Assembly Defect
A gasket that was not properly seated during factory assembly or a loose exhaust connection can create a leak that affects O2 sensor accuracy.
4. Catalytic Converter Manufacturing Defect
A rare possibility on a new vehicle, but a defective converter substrate from the factory is possible and fully warranty-covered.
How to Diagnose the P0420 Code
- Schedule a Subaru dealer appointment — all diagnosis should be warranty-covered
- Dealer checks for TSBs and ECU software updates specific to the 2024 Crosstrek
- Live data monitoring of upstream and downstream O2 sensors
- Exhaust system visual and smoke test inspection
- Converter efficiency testing if other causes are ruled out
Repair Options and Costs
Warranty Repair (Recommended)
- ECU software update: No cost under warranty
- O2 sensor replacement: No cost under warranty
- Exhaust repair: No cost under warranty
- Catalytic converter replacement: No cost under warranty
Out-of-Warranty Reference Costs
- Catalytic converter: $800–$1,500 parts and labor
- O2 sensor: $150–$280
- Exhaust leak repair: $100–$300
DIY Considerations
Do not attempt DIY repairs on a 2024 Crosstrek. All P0420-related work should be handled by an authorized Subaru dealer under warranty.
Cost Breakdown Summary
- Under warranty: $0 for all P0420 repairs
- Future reference — OEM converter: $400–$1,000
- Future reference — O2 sensor: $55–$140
Prevention Tips
- Follow Subaru's recommended maintenance schedule from day one
- Use 0W-20 full synthetic oil as specified
- Keep ECU software updated through regular dealer visits
- If using the Crosstrek off-road, be aware of the exhaust system's exposure to debris and water crossings
- Use Top Tier gasoline for optimal combustion quality