P0418 on Subaru: How to Diagnose & Fix
Secondary Air Injection System Relay A Circuit
2 Subaru models · 2 documented issues · 1 critical · $700-$2,200 repair
P0418 on Subaru by model: symptoms, diagnosis and fix
Turbo EJ255/EJ257 WRX models equipped with the secondary air injection system commonly develop failures of the air pump, pressure sensor, or the air switching valves. Moisture intrusion and corrosion can cause the valves to stick or the pump to seize, which sets emissions faults and on many cars can reduce power or force a limp-home condition. Owners typically report a check-engine light shortly after cold start, often with rough cold operation or an audible pump noise before failure.
Common Symptoms
- check engine light after cold start
- reduced power or limp mode
- loud buzzing or whining from air pump area
- rough cold start
- failed emissions inspection
How to Fix
Diagnosis usually starts with scanning for secondary air system codes and commanding the pump/valves with a capable scan tool. Repair typically involves replacing one or both air switching valves, the pump, and sometimes the pressure sensor or related hoses; some owners also inspect for water entry and update gaskets/hoses during repair. Because access is tight on turbo models, labor can be significant, and clearing codes without fixing the root cause usually results in repeat faults.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Subaru 14828AA060 Secondary Air Pump Assembly
early pump branch only after bidirectional testing proves the pump itself failed Fitment/availability: 2007 WRX and 2007 STI turbo secondary-air system; also cataloged for 2007-2008 Forester XT, confirm VIN Fitment/availability: Ships di…
- Genuine Subaru 14828AA050 Secondary Air Injection Pump Assembly
later pump branch only after bidirectional testing proves the pump itself failed Fitment/availability: 2008-2014 WRX and 2008-2021 STI; this canonical card uses it only for the 2008-2014 WRX/STI overlap, confirm VIN Fitment/availability:…
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipUse an OBD-II scanner that can read Subaru-specific pending/history codes and active test the air pump/valves before buying parts.
On turbocharged Forester XT models, the relay controlling the secondary air injection (SAI) pump can fail in the closed position, leaving the air pump running continuously. Sustained operation overheats the pump, which can melt surrounding components and create a fire risk even with the vehicle parked. Subaru recalled about 100,000 turbo vehicles (Forester XT, Impreza WRX/STI, Legacy/Outback turbo) for the defect.
Common Symptoms
- Burning / melting smell from engine bay
- Air pump audibly running after engine warmed up or off
- Check engine light with SAI codes
- Blown SAI-circuit fuse
How to Fix
Free recall repair under Subaru campaign WTM-73 (NHTSA 16V-738): the dealer replaces the secondary air injection pump relay. If the pump itself was already damaged by prolonged overheating it is replaced as well. Owners of turbo XT models should confirm the recall has been completed by VIN, as completion rates on older vehicles are often incomplete.
Find a Subaru dealer
Choose to share your location for this search, or enter an area below. Your search location is sent to Google to find dealers.
Open Subaru dealer map in Google Maps ↗Call to confirm they service Subaru vehicles and check your VIN, recall eligibility, parts availability, and appointment options.
Sources for this issue (3)
P0418 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0418 mean on a Subaru?
P0418 stands for "Secondary Air Injection System Relay A Circuit." This code means the Engine Control Module detected a fault in the control circuit for Secondary Air Injection (AIR) System Relay 'A'. The secondary air injection system pumps fresh air into the exhaust during cold starts to help the catalytic converter heat up faster and burn off pollutants, and Relay A switches power to that air pump. P0418 sets when the computer commands the relay but sees an abnormal voltage or no response on its control circuit. This is an emissions-related fault that may keep the air pump from running when needed. On Subaru it is documented across 2 models: WRX, Forester.
What are the most common causes of P0418?
The most common causes of P0418 are: Faulty secondary air injection relay (Relay A), Open, shorted, or corroded relay control wiring, Poor power or ground feed to the relay, Failed secondary air injection pump (drawing wrong current), Corroded relay socket or connector, Blown fuse in the air injection circuit, Faulty ECM relay driver. The specific cause varies by vehicle.
How much does it cost to fix P0418 on a Subaru?
Published repair estimates on Subaru range from $700 to $2,200 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0418 on a different make?
View P0418 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.