P0442 on Subaru: How to Diagnose & Fix
Evaporative Emission Control System Leak Detected (Small Leak)
2 Subaru models · 3 documented issues · $20-$900 repair
P0442 on Subaru by model: symptoms, diagnosis and fix
P0455 indicates a large (gross) EVAP leak — the system can't hold pressure/vacuum at all during the self-test. Across the Subaru lineup (Outback, Forester, Impreza, Crosstrek) the standout pattern is the purge control solenoid valve failing due to internal seal degradation, which leaves the system effectively open. The other frequent Outback source is the charcoal canister assembly behind the left-rear wheel: later Outbacks integrate a leak-check valve mounted on the canister, and a stuck/failed valve or a cracked canister triggers P0455. A badly missing, cross-threaded, or grossly leaking gas cap will also set it. Unlike the small-leak P0442, a gross leak often comes with a noticeable fuel-vapor smell near the tank/filler.
Common Symptoms
- Check engine light
- Fuel/gas smell near tank or filler
- Slightly reduced fuel economy
- No lasting drivability problem
How to Fix
Verify the gas cap is present, correct, and sealing. Smoke-test the EVAP system — apply smoke at the purge line and watch where it escapes. Most Outback fixes are replacing the purge control solenoid valve; if the leak is at the rear, drop the left-rear wheel-well liner to access and replace the charcoal canister / leak-check valve assembly. Inspect vapor lines for cracks or disconnection.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Subaru 42031AJ001 Fuel Filler Cap
only for a missing cap or one that fails inspection/seal testing Fitment/availability: 2010-2012 Outback all listed engines; confirm VIN Fitment/availability: ships in 1-2 business days with Add to Cart live when reviewed
- Genuine Subaru 42031FJ001 Fuel Filler Cap
later cap only when the cap is the proven gross leak Fitment/availability: 2013-2022 Outback branch within this card, all listed engines; confirm VIN Fitment/availability: Add to Cart live when reviewed
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (3)
P0442 means the ECM detected a small leak in the sealed evaporative-emissions system during its self-test. On the Outback the three usual culprits, in order, are: (1) the fuel filler cap — its rubber O-ring hardens and cracks with age, or the cap isn't clicked tight, or a non-OEM cap seals poorly; (2) the EVAP purge valve (solenoid), which should hold vacuum but starts to weep past its internal seal; and (3) the vent valve on/near the charcoal canister, which can't seal during the leak test if dirt or corrosion is present. Because the leak is tiny, drivers usually notice nothing but the check-engine light, and the code is often intermittent (comes and goes with temperature and fuel level).
Common Symptoms
- Check engine light (often intermittent)
- No drivability change
- Occasional faint fuel smell
- Code may clear itself then return
How to Fix
Start with the cheapest fix: inspect the gas cap, make sure it clicks, and replace it with an OEM cap if the O-ring is cracked or the cap is aftermarket. Clear the code and re-drive. If it returns, smoke-test the EVAP system to pinpoint the leak, then replace the purge solenoid or vent valve as indicated. Check vapor hoses and the canister connections for cracks.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Subaru 42031AG00A Fuel Filler Cap
cap only after inspection or seal testing proves the original cap failed Fitment/availability: 2005-2009 Outback 2.5, 2.5 turbo and 3.0 H6 branches; confirm VIN Fitment/availability: ships in 1-3 business days with Add to Cart live when …
- Genuine Subaru 42031AJ001 Fuel Filler Cap
middle-generation cap only after a failed cap test Fitment/availability: 2010-2012 Outback all listed engines; replaces 42031AJ000, confirm VIN Fitment/availability: ships in 1-2 business days with Add to Cart live when reviewed
- Genuine Subaru 42031FJ001 Fuel Filler Cap
later cap only after a failed cap test Fitment/availability: 2013-2022 Outback branch within this card, all listed engines; replaces 42031FJ000, confirm VIN Fitment/availability: Add to Cart live when reviewed
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (3)
Rust-belt GD-chassis WRX models are known for corrosion of the steel fuel filler neck and vent tubes behind the left rear wheel area. As the neck rusts through, owners notice a raw fuel smell, difficulty filling the tank, or EVAP leak codes from the compromised venting system. Subaru issued recalls and service campaigns on related Impreza models in salt-belt states because the corrosion could lead to fuel leakage.
Common Symptoms
- raw fuel smell near left rear of car
- check engine light with EVAP leak code
- difficulty filling fuel tank
- visible rust on filler neck
- fuel seepage after fill-up
How to Fix
Inspect the filler neck and vent pipes by removing the left rear wheel and splash shield, looking for rust perforation, dampness, or fuel staining. Repair usually requires replacing the filler neck assembly and associated hoses/clamps; heavily corroded fasteners may need cutting. After repair, clear EVAP codes and verify the system seals with a smoke test.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Subaru 42066FE100 Fuel Filler Pipe
complete rear filler pipe after corrosion/perforation is confirmed Fitment/availability: 2005-2007 Impreza WRX filler-neck branch; supersedes 42066FE060, confirm VIN and associated hoses/clamps Fitment/availability: ships in 1-3 business…
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
- TipCheck recall eligibility by VIN first, especially for cars originally sold in salt-belt states.
P0442 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 P0442 mean on a Subaru?
P0442 stands for "Evaporative Emission Control System Leak Detected (Small Leak)." This emissions code means the evaporative emission (EVAP) control system has detected a small leak. The EVAP system seals the fuel tank and captures gasoline vapors, routing them to be burned in the engine instead of escaping into the air, and the computer periodically pressure- or vacuum-tests the system to confirm it's sealed. A small leak the size of about a 0.040-inch hole will set this code. By far the most common and cheapest cause is a loose, damaged, or missing gas cap, so that's the first thing to check, though any cracked hose or worn seal in the system can also trigger it. On Subaru it is documented across 2 models: Outback, WRX.
What are the most common causes of P0442?
The most common causes of P0442 are: Loose, damaged, or missing fuel filler cap, Worn or cracked gas cap seal, Cracked or disconnected EVAP hose or line, Faulty purge valve or vent valve, Damaged O-ring or seal at the fuel tank or filler neck, Small crack in the charcoal canister, Leaking fuel tank sending unit gasket. The specific cause varies by vehicle.
How much does it cost to fix P0442 on a Subaru?
Published repair estimates on Subaru range from $20 to $900 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 P0442 on a different make?
View P0442 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.