Fuel filler cap loose, worn, damaged or wrong type, or with a perished seal; Cracked, split or perished EVAP hoses or loose or hardened connections and clips; Purge valve (canister purge solenoid) sticking partly open or leaking; Vent valve or shut-off valve not sealing properly; Damaged or corroded filler neck, or a leaking fuel tank seal or sender unit gasket; Cracked or leaking carbon canister; Faulty fuel tank pressure sensor giving incorrect readings, or a faulty leak detection pump where fitted.

P0442

EVAP System Leak Detected (small leak).

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
4: AreaAuxiliary emission controls
42: FaultThe specific fault in that area

What it means

P0442 means the engine control unit ran an evaporative emission (EVAP) system leak test and found a small leak in the system that traps fuel vapour from the tank. The test usually seals the system and applies vacuum or pressure, and the code sets when the pressure change or decay is greater than expected but only by a small amount, typically equivalent to a hole of around 0.5 mm. The leak can be anywhere from the filler cap to the purge valve, so it needs tracing methodically.

Symptoms

Engine management light on
Faint fuel smell around the car or fuel filler area
No obvious change in driveability in most cases
Possible fuel cap warning message on some models
Failed emissions test at inspection time

Possible causes

Fuel filler cap loose, worn, damaged or wrong type, or with a perished seallikely
Cracked, split or perished EVAP hoses or loose or hardened connections and clipslikely
Purge valve (canister purge solenoid) sticking partly open or leakinglikely
Vent valve or shut-off valve not sealing properlypossible
Damaged or corroded filler neck, or a leaking fuel tank seal or sender unit gasketpossible
Cracked or leaking carbon canisterpossible
Faulty fuel tank pressure sensor giving incorrect readings, or a faulty leak detection pump where fittedrare

How to diagnose

Read the stored codes and freeze frame data, noting fuel level, temperature and whether other EVAP or fuel trim codes are present.
Inspect the fuel cap for a damaged seal, cracks or incorrect fit, and check that it clicks or tightens properly.
Visually inspect the filler neck, the accessible EVAP hoses, connectors and clips for damage, perishing or looseness, including around the canister and purge valve.
Check the purge valve and vent valve electrical connectors and wiring, and test the valves for correct operation and for sealing when de-energised, following the manufacturer's procedure.
Use the scan tool's EVAP system test or live data, where supported, to check tank pressure sensor readings against known conditions.
Perform a smoke test of the EVAP system at the correct low pressure to locate the leak, rather than guessing at parts.
Inspect the tank, sender unit seal and canister for damage or leaks once smoke or pressure testing has pointed to that area.
Clear the code after repair and run the monitor drive cycle to confirm it passes, as the test conditions vary by model and engine.

How to fix

Replace the fuel cap with the correct type if it is damaged, worn or not sealing.
Replace cracked or perished EVAP hoses, or refit and replace loose or damaged clips and connections.
Replace a faulty purge valve or vent valve.
Repair or replace a damaged filler neck, or renew a leaking tank sender seal or gasket.
Replace a cracked carbon canister.
Replace a faulty tank pressure sensor or leak detection pump only after testing confirms it is at fault.

Can I keep driving?

Low severity

The car is generally safe to keep driving, as a small EVAP leak does not normally affect engine running. Book it in to be fixed, particularly if you can smell fuel or need to pass an emissions test.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.