01 Why Your Car Cranks But Doesn't Start • 02 Free VIN Check: Top 10 Free Sites to Get a Used Car's Histo… • 03 Fix This First If Your Car Won’t Start (Before Calling a Me… • 04 Decoding the Engine Control Unit (ECU): Inputs, Outputs, an… • 05 This Is Why You’ll Want an Electric Car by 2030 • 06 Should You Admit Fault in a Car Accident if It's Your Fault? • 07 This Is Why Your Car’s EGR Valve Is Stuck • 08 How To Fix Automatic Transmission Not Shifting • 09 Important Safety Recall: Ford Recalls 1 Million Vehicles fo… • 10 The Future of Autonomous Vehicles •

DTC codes / P04xx · Auxiliary emission controls / P0442

P0442EVAP System Leak Detected (Small)

P0442 means the engine computer detected a small leak in the evaporative emission control (EVAP) system, which captures fuel vapor instead of letting it escape into the atmosphere. During a self-test, the computer pressurizes or pulls a vacuum on the sealed fuel system and measures how quickly pressure bleeds off; a small leak falls within a narrow threshold, typically equivalent to a hole about 0.04 inch (1 mm) across.

SystemPowertrain
Code typeGeneric (all makes)
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 vehicle after refueling or while parked, especially in warm weather.
  • The check engine light may clear itself after several drive cycles and then return, since the EVAP monitor only runs under specific conditions.
  • Slightly increased fuel odor in the engine bay or near the fuel tank if the leak is under the hood or at the tank.
  • No drivability complaints such as rough idle, misfire, or power loss, which helps distinguish this from engine-related codes.

Common causes, most likely first

  1. A loose, damaged, or missing fuel filler cap, or a cap with a cracked or hardened seal.
  2. A cracked or disconnected EVAP hose or vapor line, often at a plastic connector or where a line bends near the tank or canister.
  3. A faulty purge solenoid or vent solenoid that does not seal fully when commanded closed.
  4. A leaking fuel tank pressure sensor seal or a sensor that misreports pressure during the monitor.
  5. A small crack in the EVAP canister or a damaged canister purge port.
  6. A leaking fuel tank seam, filler neck, or fuel pump module gasket, which is less common but possible on older vehicles.
  7. A stuck or leaking check valve in the EVAP system that prevents the system from holding pressure or vacuum.

How to diagnose and fix it

  1. Inspect the fuel filler cap first: check that it is present, tightens properly, and has an intact rubber seal, then clear the code and drive through a full EVAP monitor cycle.
  2. Visually inspect all visible EVAP hoses and lines under the hood and near the fuel tank for cracks, loose connections, or rubbing damage.
  3. Use a scan tool to command the EVAP system through its tests and watch fuel tank pressure sensor readings for signs of a slow bleed.
  4. Perform a smoke test by introducing smoke into the EVAP system with a smoke machine and look for the source of the small leak.
  5. If no leak is visible, isolate sections of the system and pressure-test them individually to narrow the fault to a hose, canister, solenoid, or tank component.
  6. Replace the confirmed faulty component, such as the filler cap, purge solenoid, vent solenoid, or a cracked hose, then clear codes and verify the monitor completes.
  7. After repair, drive the vehicle through the required enable conditions so the EVAP monitor runs and confirms the code does not return.

Small EVAP leaks that fool good technicians

  • A fuel filler cap that looks fine can still leak at the seal, so always test or substitute the cap before chasing hoses and solenoids.
  • The EVAP monitor only runs when the fuel level is between roughly one-quarter and three-quarters full, so a code that appears only after refueling points toward the cap or filler neck area.
  • A smoke test can miss a leak that only appears when a solenoid is commanded closed, so testing the system in its sealed state matters as much as finding visible smoke.
  • P0442 is sometimes set by a fuel tank pressure sensor that reads inaccurately rather than by a real leak, so compare sensor readings against a known-good reference before replacing hardware.
  • After any EVAP repair, the code may not clear immediately because the monitor needs specific temperature and fuel-level conditions, so a returning light after a few days is not always a failed repair.

Can I keep driving with P0442?

It is safe to keep driving with P0442 because a small vapor leak does not affect engine performance or safety, but have it diagnosed reasonably soon to prevent a larger leak from developing. Avoid topping off the fuel tank past the automatic shutoff, since that can force liquid fuel into the EVAP system and worsen the leak.

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 all OBD-II 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