P0442: Evaporative Emission System Leak Detected (Small Leak)
Title: SAE J2012 generic definition. Manufacturer-specific definitions and enhanced codes can differ; check service information for the exact vehicle.
What P0442 means
The EVAP system, which stores fuel vapor and burns it in the engine, failed its leak test with a small leak.
What sets it
With the vent valve closed, the ECM either pulls a vacuum on the sealed fuel tank and vapor system or (on some systems) uses a pump, and watches how well it holds. California's OBD II rules define the small-leak target as a leak equal to a 0.040-inch hole. The manufacturer's test threshold applies to each vehicle (general guideline only).
Symptoms
- Usually no drivability symptoms
- Occasional faint fuel smell
- Failed emissions inspection
Is it safe to drive?
General guidance, not a guarantee: Generally safe to drive. A strong raw-fuel smell is different: find the source promptly, because liquid fuel leaks are a fire risk. If in doubt, have it towed and diagnosed.
Common causes
Listed roughly from most to least common in general practice. The real order varies by vehicle, mileage and history.
- Gas cap seal worn or cap not seated
- Cracked or loose EVAP hose
- Purge or vent valve not sealing
- Filler neck rust or seal leak
- Charcoal canister or tank seal
Test before you replace: diagnostic sequence
General guidance only. Always follow the vehicle manufacturer's service information, specifications and safety procedures. Any figures below are general guidelines that defer to the manufacturer's specification.
- Inspect the gas cap seal and filler neck. Replace the cap only if it is damaged or the wrong part.
- Smoke-test the EVAP system at the service port, or per the manufacturer's procedure, with the vent closed.
- Look closely at the filler neck, the hoses at the tank and the canister area, where leaks are common.
- Command the vent and purge valves with the scan tool and confirm each one seals and opens.
- After repair, run the EVAP self-test where supported, or complete the monitor's enable conditions. These often include a fuel level window and a cold soak, which is why the EVAP monitor can take days to run.
Bench note: A small leak can be hard to see with smoke. Give the smoke time, use a bright light, and check the top of the tank and the filler neck.
How-to guides for this code
Related codes
FAQ
Is P0442 just the gas cap?
Sometimes, but not always. Check the cap seal, then smoke-test. Replacing caps over and over without testing wastes money.
Why won't the EVAP monitor run?
EVAP tests often need a cold start, a certain fuel level and a period of steady driving. Check the manufacturer's enable conditions.
What size is a "small leak"?
California's OBD II regulation describes the target as a 0.040-inch hole. Each manufacturer calibrates its own test.
Sources
- SAE J2012, Diagnostic Trouble Code Definitions (standard page; code titles only)
- California Code of Regulations, 13 CCR 1968.2, OBD II requirements (via Cornell LII)
- California Air Resources Board, On-Board Diagnostic (OBD) program
- US EPA, "What To Do With the Check Engine Light" (EPA420-F-00-041)
Written with AI assistance and reviewed for accuracy; not a substitute for OEM service information. Shop Docs Studio is not affiliated with SAE, EPA, CARB or any vehicle manufacturer.