Catalytic converter failure, commonly indicated by a P0420 check engine light, reduces engine performance and increases emissions due to an inefficient or damaged catalytic converter.
Reviewed by SubaruReview Editorial Team · Last reviewed 2026-05-15 · Editorial standards
How this problem ranks against the other documented Outback failures — cost, severity, and DIY difficulty at a glance.
| Problem | Years | Severity | Repair cost | DIY |
|---|---|---|---|---|
| Catalytic Converter Failure (P0420) (this page) | 2010-2019 | Major | $1,500–$2,500 | 3/5 |
| EJ25 SOHC Head Gasket Failure | 1999-2009 | Major | $1,800–$3,200 | 4/5 |
| Excessive Oil Consumption | 2011-2015 | Major | $3,500–$5,500 | 1/5 |
| Subaru Outback DPF Regeneration Failure & Clogging | 2010-2015 | Major | $800–$3,500 | 4/5 |
This is one of several documented Outback problems we track, and it fits inside the broader Engine Guides guide. If you're weighing repair against replacement, cross-check the Subaru repair-cost database and any open NHTSA recalls on your VIN before booking a shop.
The catalytic converter is a crucial component in your exhaust system, responsible for converting harmful pollutants into less toxic gases. When it fails, often due to degradation of the internal catalyst material, it can restrict exhaust flow and prevent the engine from running efficiently. This often triggers a P0420 diagnostic trouble code, indicating that the catalyst system efficiency is below the threshold.
Over time, catalytic converters can degrade due to oil or coolant contamination, exhaust rich conditions (often from misfires), or simply age and mileage. The internal ceramic honeycomb structure, coated with precious metals like platinum, palladium, and rhodium, can melt or break apart, leading to reduced efficiency or blockages.
Over time, catalytic converters can degrade due to oil or coolant contamination, exhaust rich conditions (often from misfires), or simply age and mileage. The internal ceramic honeycomb structure, coated with precious metals like platinum, palladium, and rhodium, can melt or break apart, leading to reduced efficiency or blockages.
National average $1,500–$2,500. Cost varies significantly based on whether an OEM or aftermarket catalytic converter is used, and labor rates in your area. Some states have stricter emissions requirements, which might necessitate more expensive, compliant catalytic converters.
Difficulty 3/5. Replace the faulty catalytic converter with a new OEM or high-quality aftermarket unit. Ensuring proper engine tune-up and addressing any underlying issues that may have contributed to the converter's failure (e.g., misfires, oil consumption) is crucial for longevity.
Check Engine Light (P0420); Reduced engine power; Poor fuel economy; Sulfur or rotten egg smell from exhaust; Failed emissions test; Rattling sound from underneath the vehicle
Owners typically pay $1,500–$2,500 at an independent Subaru shop, parts and labor included. Our Subaru Oxygen Sensor Replacement Cost guide breaks the job down by parts, labor hours, and where the money actually goes.
The same generation also sees EJ25 SOHC Head Gasket Failure and Excessive Oil Consumption. Both are documented with symptoms, cost, and a permanent-fix walkthrough — see the full list in the Outback hub.
We rate it 3/5 on our DIY scale. Confident wrenchers can tackle it in a weekend using the permanent-fix steps above. Cross-reference the reliability & common problems hub for related jobs worth bundling while you're in there.
Dig into the Problems Database to plan your next maintenance sprint, or browse every model hub for buyer's guides, generation breakdowns, and known-issue lists.