P0442 · Evaporative Emission Control System Leak Detected Small Leak

Key facts

Definition and circuit logic

• Evaporative Emission Control System Leak Detected Small Leak

First-fault record

• When P0442 first sets, preserve engine speed, load, vehicle speed, coolant temperature, fuel level and system voltage.
• Separate current, pending, permanent and history status and capture companion codes from the same event.

Diagnostics and measurement

Symptoms

• The malfunction indicator may illuminate while drivability can remain normal in many applications.
• The EVAP readiness monitor may not complete.

Freeze frame and initial capture

• When P0442 first sets, preserve engine speed, load, vehicle speed, coolant temperature, fuel level and system voltage.
• Separate current, pending, permanent and history status and capture companion codes from the same event.

Common diagnostic mistakes

• Do not treat the code as an instruction to replace a cap, valve or sensor; verify sealing, command and feedback first.
• Do not exceed manufacturer-approved low test pressure during smoke testing.

Post-repair verification

• After repair, reproduce the EVAP monitor enabling conditions when practical.
• Recheck pending/permanent DTC status and tank-pressure/purge response.

Safety

• Fuel vapor is flammable; avoid sparks, open flame and unapproved pressure sources.
• Follow manufacturer safety procedures when working around the fuel tank and EVAP system.

Possible causes

• Fuel-cap or filler-neck sealing, EVAP hose/connection, canister, purge valve or vent valve leakage.
• Tank-pressure sensor rationality or failure to seal the system during the monitor.

Live data to monitor

• Tank/EVAP pressure sensor, purge command and vent command.
• Fuel level, ambient temperature and monitor enabling conditions.

Measurement sequence for a DTC

1. Record which module stored the code and under what conditions.
2. Review freeze-frame and simultaneous codes together.
3. Verify power, ground and voltage-drop basics.
4. Compare commanded and actual values in live data.
5. Recreate the operating condition after repair.