Emission controls · Powertrain · generic (SAE-defined)
P0442: Evaporative Emission System Leak Detected (Small Leak)
P0442 means the engine computer has found a small leak in the evaporative emission (EVAP) system, which is supposed to stay sealed to trap fuel vapor.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0442 sets
During its leak test, typically after the vehicle has sat and the fuel level is within a set range, the powertrain control module (PCM) closes the canister vent valve and either draws a vacuum through the purge valve or uses a leak detection pump to pressurize the system. It then watches the fuel tank pressure or pump response. If pressure or vacuum decays faster than allowed for a sealed system, but not fast enough to indicate a large leak, the PCM sets P0442. Many systems are designed to detect leaks equivalent to a hole around 0.040 inch, but test details are manufacturer-specific.
Common causes of P0442
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Worn, cracked, or improperly tightened fuel cap seal
- Cracked or loose EVAP hoses and connections
- Leaking purge valve or vent valve
- Cracked charcoal canister
- Rusted or damaged fuel filler neck
- Leaking fuel pump module or sender seal on the tank
- Faulty leak detection pump or tank pressure sensor
P0442 symptoms
- Check engine light on
- Faint fuel smell in some cases
- No change in drivability
- Failed emissions inspection
How P0442 is diagnosed
- Start with the fuel cap: inspect the seal, ensure it clicks tight, and confirm it is the correct cap for the vehicle
- Scan for other EVAP codes and check freeze frame conditions
- Visually inspect accessible EVAP hoses, the canister, and the filler neck for cracks, rust, or loose fittings
- Perform a smoke test on the EVAP system with the vent sealed to locate the leak
- Command the vent valve closed and check that it seals; command the purge valve and check that it does not leak when closed
- Inspect the fuel pump module seal and tank top fittings if no other leak is found
- After repair, run the EVAP monitor or complete drive cycles to confirm the fix
Typical fixes for P0442
- Replace a worn fuel cap with a correct-fit cap
- Replace cracked hoses or loose connections
- Replace a leaking purge or vent valve
- Replace the charcoal canister or filler neck
- Reseal the fuel pump module or tank fittings
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Very common across most makes. Leak detection methods differ: some use engine vacuum, others use a dedicated pump or natural vacuum leak detection; check factory service information.
Related codes & warning lights
P0442 FAQ
What does code P0442 mean?
P0442 means the engine computer has found a small leak in the evaporative emission (EVAP) system, which is supposed to stay sealed to trap fuel vapor. The standard definition is "Evaporative Emission System Leak Detected (Small Leak)."
Can I drive with a P0442 code?
Yes. A small EVAP leak does not affect engine operation or safety in normal circumstances. Repair it to stop vapor emissions and to pass inspection, and investigate promptly if you smell raw fuel.
Is a loose gas cap really enough to set P0442?
Yes. A cap that is not fully tightened or has a worn seal is one of the most common causes. If the cap is fine, a smoke test is the most reliable way to find the leak.
How long after fixing P0442 will the light go off?
The light usually turns off after the EVAP monitor runs and passes on several drive cycles. Because the test often needs an overnight cold soak and a certain fuel level, this can take several days.
Why does P0442 come back in hot weather?
Temperature changes affect vapor pressure in the tank, and a marginal seal or small crack may only leak enough to fail the test under certain conditions.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.