What Does Code P0420 Mean on a 2022 Subaru WRX?
A P0420 code on your 2022 Subaru WRX means the ECU has detected that the Bank 1 catalytic converter is underperforming. The 2022 WRX marks a new generation, powered by the 2.4L FA24F turbocharged boxer-4 engine producing 271 horsepower and 258 lb-ft of torque. It is available with either a 6-speed manual or the Subaru Performance Transmission (SPT) CVT, both with Symmetrical AWD.
The WRX's performance-oriented turbo engine runs at high exhaust temperatures, and P0420 is a concern that WRX owners should take seriously. Aftermarket modifications are also a common trigger for this code.
Common Symptoms
- Check engine light on (steady)
- Slight reduction in fuel economy from the rated 22 city/28 highway MPG
- Sulfur or rotten egg smell from exhaust
- Emissions test failure
- Usually no noticeable power loss unless converter is severely clogged
Most Likely Causes on the 2022 WRX
1. Aftermarket Exhaust or Tune Effects
Many WRX owners install aftermarket downpipes, exhausts, or engine tunes. These modifications can trigger P0420 by altering exhaust flow or removing the catalytic converter entirely. If your WRX is modified, this is the most likely cause.
2. Failing Catalytic Converter
The WRX's turbo engine produces high exhaust temperatures, especially during spirited driving. This heat stress, combined with the boost pressure, can accelerate converter degradation faster than a naturally aspirated engine.
3. Faulty Downstream O2 Sensor
The rear oxygen sensor on the turbo WRX is subjected to extreme heat cycling. It can become sluggish or fail, especially if the vehicle is driven hard regularly.
4. Boost or Wastegate Issue
A malfunctioning wastegate or boost leak can alter the air-fuel ratio, sending excess unburned fuel through the catalytic converter and damaging it. Check for boost-related codes alongside P0420.
How to Diagnose the P0420 Code
- Verify the exhaust system is fully stock — any modifications can cause P0420
- Scan for all codes, especially boost, misfire, and fuel trim codes
- Monitor live data from upstream and downstream O2 sensors
- Inspect the turbo downpipe, wastegate, and all exhaust connections for leaks
- Test catalytic converter efficiency with temperature differential measurement
Repair Options and Costs
Professional Repair
- Catalytic converter replacement: $1,000–$2,000 parts and labor
- Downstream O2 sensor: $160–$320
- Exhaust leak repair: $150–$400
- Return to stock exhaust (if modified): $200–$500 labor
DIY Considerations
WRX owners tend to be hands-on. O2 sensor replacement is feasible. If the vehicle has aftermarket exhaust components, returning to stock may resolve the code. Catalytic converter replacement on the turbo WRX requires experience with the downpipe-to-converter connection.
Cost Breakdown Summary
- OEM catalytic converter: $600–$1,400
- Aftermarket CARB-compliant converter: $300–$700
- O2 sensor (part): $60–$170
- Labor: $250–$600
- Diagnostic fee: $100–$150
Prevention Tips
- If running an aftermarket tune, ensure it includes proper catalyst monitoring adjustments
- Use premium 93 octane fuel as recommended for the turbo engine
- Allow the turbo to cool down after spirited driving — idle for 30-60 seconds before shutdown
- Replace spark plugs at the recommended interval for the turbo engine
- Avoid running a catless downpipe on a street-driven vehicle — it guarantees P0420