P2440 on Subaru: How to Diagnose & Fix
Secondary Air Injection System Switching Valve Stuck Open (Bank 1)
1 Subaru model · 1 documented issue · $600-$2,200 repair
P2440 on Subaru by model: symptoms, diagnosis and fix
Subaru WRX STI models equipped with the EJ257 and secondary air injection commonly develop failures of the air pump and/or the air switching valves, often due to moisture intrusion and internal corrosion that causes the valves to stick. Owners typically see a check engine light with cold-start drivability changes and may fail emissions/inspection due to stored air injection codes. This issue is widely documented in owner reports and Subaru service information/TSBs covering secondary air injection diagnostics and component replacement.
Common Symptoms
- Check Engine Light on after cold start
- DTCs P0410, P2440/P2441/P2442/P2443 stored
- Rough or high idle on cold start
- Failed emissions/inspection readiness
- Whining or abnormal noise from air pump area
How to Fix
Diagnose with scan tool and active tests; replace failed air pump and/or air switching valves and related hoses/gaskets. Common components include the secondary air pump and air switching valves (bank-specific); replace any water-damaged connectors and ensure updated routing/sealing per Subaru service guidance (refer to Subaru TSBs addressing secondary air injection DTCs for applicable years).
What you need to diagnose it
The repair instructions explicitly call for reading stored codes. Use a scanner that can read the named code families before choosing a repair.The recommended scanner supports these code families; confirm your exact year, model and module coverage before buying.
ANCEL AD310 Classic OBD-II Scanner
Read & clear engine (P) codes
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Reading and clearing the code is DIY work. Module replacement or reprogramming is not — most modules are VIN-programmed, so a new one does nothing until a shop codes it to your car. Check for an open recall or service bulletin before buying anything.
Sources for this issue (1)
P2440 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 P2440 mean on a Subaru?
P2440 stands for "Secondary Air Injection System Switching Valve Stuck Open (Bank 1)." P2440 indicates the secondary air injection (SAI) system's switching/diverter valve on engine bank 1 is stuck open. The secondary air system briefly pumps fresh air into the exhaust at cold start so the catalytic converter heats up and lights off faster, cutting cold-start emissions. The computer commands this valve closed once warm-up is done; if it senses the valve hasn't closed (air is still flowing when it shouldn't be), it sets this code. A stuck-open valve can let exhaust pressure or moisture back into the air pump and skews the oxygen sensor readings during warm-up. On Subaru it is documented across 1 model: WRX STI.
What are the most common causes of P2440?
The most common causes of P2440 are: Air switching/diverter valve stuck open or seized, Carbon, rust, or debris fouling the valve, Faulty valve vacuum control solenoid or leaking vacuum line, Corroded or moisture-damaged secondary air pump, Wiring or connector faults at the valve solenoid, Clogged or failed combination/check valve, Vacuum leak preventing the valve from closing. The specific cause varies by vehicle.
How much does it cost to fix P2440 on a Subaru?
Published repair estimates on Subaru range from $600 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 P2440 on a different make?
View P2440 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.