OBD-II trouble code
P0442: Evaporative Emission System — Small Leak Detected
The engine computer detected a small leak in the evaporative emission (EVAP) system. The check engine light is on but the car runs normally. The most common cause is a worn gas cap or a small crack in an EVAP hose.
Quick facts
- System
- Powertrain
- Category
- Emissions / EVAP
- Severity
- Low severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $20 – $500
- DIY difficulty
- Beginner DIY
What does P0442 mean?
The evaporative emission (EVAP) system traps fuel vapors from the gas tank and routes them into the engine to be burned. The engine control module (ECM) periodically self-tests the system by sealing it and monitoring pressure or vacuum decay. A small leak — typically equivalent to a 0.020-inch opening — is detected when pressure decays faster than expected but slower than a large leak would cause.
P0442 is the "small leak" code in the EVAP family. P0455 covers a large leak, P0456 covers a very small leak on some manufacturer-specific systems, and P0440 is the general EVAP malfunction code on older vehicles.
Small leaks are harder to find than large ones because the source is often a tiny crack, a worn seal, or a slowly seeping valve. The fix usually costs less than $200, but locating the leak typically requires a smoke test at a shop. The vehicle runs normally and will not strand you — the consequence is failing an OBD-II emissions inspection.
Common causes
- Worn or improperly seated gas cap (very common)
- Small crack in an EVAP hose, often from age or rodent damage
- Slow-seeping purge valve or vent valve
- Hairline crack in the charcoal canister housing
- Fuel tank sending unit gasket seeping
- Cracked or loose fitting on a tank pressure sensor
Symptoms
- Check engine light is on
- Possible faint fuel smell, especially in warm weather
- Failed OBD-II emissions inspection
- No driveability symptoms or change in performance
Diagnostic steps
- 1.Replace or properly seat the gas cap. Drive three to five complete drive cycles and rescan.
- 2.Visually inspect EVAP hoses for cracks, brittleness, or rodent damage.
- 3.Smoke-test the EVAP system. A smoke machine is the most reliable way to find a small leak.
- 4.Use a scan tool to monitor purge and vent valve operation and duty cycles. A valve that doesn't close fully will register as a small leak.
- 5.On older vehicles, check the charcoal canister for cracks and the fuel tank sending unit gasket for seepage.
Repair cost
$20 – $500
A replacement gas cap costs $15 to $40. EVAP hose replacement runs $80 to $250 including labor. A purge or vent valve replacement is $100 to $300. Smoke testing typically adds $50 to $150. Charcoal canister replacement is the most expensive likely outcome at $300 to $500.
Estimate your repair
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Open the Repair Cost Estimator with evap system repair preselected. Adjust labor rate and vehicle category to fit your situation.
Related repairs
DIY vs shop
This is a beginner-friendly repair. Common hand tools, a free afternoon, and a willingness to follow a procedure are usually enough. The risk of causing a bigger problem is low if you read up on your specific vehicle first.