A Guide to the Catalytic Converter for the 2018-2022 Subaru Impreza
Understand the common P0420 code and how to choose the right replacement catalytic converter for your Impreza.
- Always check for recalls (like WRE-21) and TSBs (like 09-110-23R) before replacing parts; a repair might be covered by Subaru.
- The P0420 code does not always mean the converter is bad; have a mechanic diagnose for exhaust leaks or faulty sensors first.
- A quality direct-fit aftermarket converter offers huge savings over an OEM part, but avoid cheap universal parts that require welding.
- It is highly recommended to replace the front and rear oxygen sensors at the same time as the converter for a complete repair.
Is Your Impreza's Catalytic Converter Failing?
If you own a 2018-2022 Subaru Impreza, the most common sign of a catalytic converter problem is a check engine light on your dashboard displaying the code P0420 (Catalyst System Efficiency Below Threshold). While this code points to the converter, it's not always the root cause. Other symptoms can include a noticeable loss of engine power, slower acceleration, or a rattling sound from under the car, which could mean the internal parts of the converter have broken apart. You might also notice a smell like rotten eggs from the exhaust or see your fuel economy get worse.
🎬 See a breakdown of the common signs of a bad converterCheck for Recalls and Service Bulletins First!
Before you buy any parts, check if your Impreza is affected by any official Subaru programs. There is a safety recall (NHTSA ID: WRE-21) for some 2017-2019 Impreza models for a faulty ignition coil. As part of this recall, if a specific trouble code is found, the dealer will replace the front exhaust pipe, including the catalytic converter, for free. Additionally, Subaru has a Technical Service Bulletin (TSB 09-110-23R) specifically for the P0420 code on 2017-2023 Imprezas, which guides technicians to check for other causes like exhaust leaks or bad sensors before replacing the converter. Always have a technician perform a full diagnosis.
🎬 Watch: How to test if you really need a new converterChoosing a Replacement: OEM vs. Aftermarket
When it's time to replace the converter, you have two main choices: a new OEM part from Subaru or a new aftermarket part from a brand like Magnaflow. The price difference is significant.
- OEM (Original Equipment Manufacturer): This is the exact part your Impreza was built with. It guarantees a perfect fit and performance. However, the cost for the complete OEM exhaust pipe assembly containing the converter can be extremely high, often running into the thousands of dollars.
- Aftermarket (Magnaflow Direct-Fit): Aftermarket parts are made by companies other than the original manufacturer. A quality, direct-fit aftermarket converter from a reputable brand like Magnaflow can be a reliable and much more affordable solution. These are designed to bolt directly into place without welding, just like the original. Be cautious of very cheap, universal-fit converters, as they may require cutting and welding and might not meet the specific requirements of Subaru's sensitive emissions system, potentially causing the P0420 code to return.
Pro Tip: Direct-Fit is Key
For a straightforward installation and better chance of success, always choose a "direct-fit" catalytic converter. This ensures all the hangers and flanges line up with your Impreza's existing exhaust system, avoiding the need for custom welding. It's also a good practice to replace the exhaust gaskets and any rusted hardware at the same time to prevent leaks.
Catalytic Converter Replacement Cost for 2018-2022 Subaru Impreza
| Part Type | Estimated Part Cost |
|---|---|
| New OEM | $2,500 - $3,100 |
| New Aftermarket (Magnaflow) | $194.00 |
| Shop Labor | $150 - $350 |
Frequently Asked Questions
Will a new aftermarket converter definitely fix my P0420 code?
Not always. The P0420 code means the converter isn't working efficiently, but the cause could be something else. An engine running rich, a bad oxygen (A/F) sensor, or an exhaust leak can all trigger the code. It's critical to diagnose the underlying problem first, as outlined in Subaru's TSB. Replacing the converter without fixing the root cause may lead to the new converter failing prematurely.
Should I replace my oxygen sensors with the catalytic converter?
It is highly recommended. The front air-fuel ratio sensor and the rear oxygen sensor work with the converter to monitor emissions. If the old converter failed due to contamination, the sensors are likely contaminated too. Replacing them ensures the entire system is working correctly and can prevent you from having to do the job twice.
Why is the OEM Subaru converter so expensive?
OEM catalytic converters contain a higher concentration of precious metals (like platinum, palladium, and rhodium) which are very expensive. These metals are what perform the chemical conversion of exhaust gases. While aftermarket converters use these metals too, they often use the minimum amount required to meet EPA standards, which helps keep their cost down.
Can I install a catalytic converter myself?
If you have mechanical experience, the right tools, and can safely lift the vehicle, a direct-fit converter replacement is a manageable DIY job. The main challenge is often dealing with rusted bolts, which may require a breaker bar or cutting tools. If you are not comfortable working under your car, it's best to leave this job to a professional mechanic.
🎬 Watch: Subaru catalytic converter replacement using basic hand toolsHelpful Videos
Technical Specifications
OEM Part Numbers: 44620AE990 44620AA78A
The 2018-2022 Subaru Impreza uses a direct-fit catalytic converter that is integrated with a section of the exhaust pipe. The system uses one upstream air-fuel ratio sensor and one downstream oxygen sensor to monitor efficiency.
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Subaru Impreza:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Is Your Impreza's Catalytic Converter Failing?
- Check for Recalls and Service Bulletins First!
- Choosing a Replacement: OEM vs. Aftermarket
- Pro Tip: Direct-Fit is Key
- Catalytic Converter Replacement Cost for 2018-2022 Subaru Impreza
- Frequently Asked Questions
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