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DTC codes / Nissan codes / P1440

P1440 · NissanEVAP Control System Small Leak

P1440 on Nissan vehicles indicates the engine computer has detected a small leak in the evaporative emission control system, which captures fuel vapor from the tank and burns it through the engine. The computer runs a vacuum-decay test and sees pressure bleed off slower than a large leak but faster than a sealed system should allow, so it flags a small leak rather than a gross one.

SystemPowertrain
Code typeNissan specific
SeverityLow
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • Often no symptoms besides the warning light, because a small vapor leak does not affect how the engine runs.
  • A faint raw fuel smell around the rear of the car or near the fuel filler after parking, especially on warm days.
  • The check engine light may come and go over several drive cycles as the monitor passes and fails intermittently.
  • Slightly increased fuel odor when refueling or when the tank is topped off.
  • No drivability complaints in most cases, though a rough idle can appear if the leak is near a purge line.

Common causes, most likely first

  1. A fuel filler cap that is loose, missing, or has a hardened or damaged seal.
  2. Cracks or splits in the rubber EVAP hoses running from the tank to the canister and purge valve.
  3. A leaking or stuck-open EVAP purge solenoid that bleeds vacuum when it should hold.
  4. A cracked or rusted EVAP canister, common on older Nissans exposed to road salt.
  5. A faulty fuel tank pressure sensor giving inaccurate readings during the leak test.
  6. A small crack in the fuel tank itself or a deteriorated seal at the fuel pump module.
  7. A leaking or improperly seated rollover valve or vent valve on the tank.

How to diagnose and fix it

  1. Inspect the fuel filler cap first: check the seal for cracks or hardening, clean the mating surface, and tighten it until it clicks.
  2. Clear the code and drive several complete drive cycles to see whether the small leak monitor passes before doing any parts replacement.
  3. Visually inspect all EVAP hoses under the hood and along the tank for cracks, loose clamps, or disconnected lines.
  4. Use a scan tool to command the purge and vent valves and watch fuel tank pressure to confirm the system holds vacuum.
  5. Perform a smoke test on the EVAP system to pinpoint the exact leak location, paying attention to the canister, filler neck, and tank seals.
  6. Test the purge solenoid for correct resistance and for sealing when de-energized, replacing it if it bleeds vacuum.
  7. If no external leak is found, check the fuel tank pressure sensor reading against a known-good value and inspect the tank and pump module seals.

Small leaks that fool good technicians

  • A small leak code often sets because the fuel filler cap was left loose at the last fill-up, so always verify cap condition and seating before chasing hoses.
  • Nissan EVAP monitors are sensitive to fuel level; testing with a tank that is too full or nearly empty can produce a false small-leak result, so run the test between one-quarter and three-quarters full.
  • A purge solenoid that sticks slightly open can bleed vacuum and mimic a small leak even when every hose and the canister are sealed perfectly.
  • The fuel tank pressure sensor on older Nissans drifts with age and can report a decay that is not real, leading to unnecessary canister replacement.
  • Smoke testing is far more reliable than guessing at hoses, because a pinhole in a line above the tank is invisible from underneath and only shows under smoke pressure.

Can I keep driving with P1440?

You can keep driving with P1440 because a small EVAP leak does not affect engine safety or performance, but avoid topping off the tank past the first click and get the system smoke-tested soon to prevent the leak from growing or allowing fuel vapor to escape.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Nissan vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage