How do I replace the fuel tank vent

Typical issues in most likely order.

1. Loose fuel cap
2. Vacuum leak (fractured or detached line)
3. Bad fuel cap (seal or vent)
4. Failing EVAP purge valve solenoid
5. Failing EVAP canister vent solenoid
6. Fuel tank pressure sensor.

The leak can be difficult to find especially if fuel tank seal or fuel vent line.

If you can DYI and given the vehicle age, replace fuel cap, purge valve solenoid, and vent solenoid. It will cost $70-$100 but you'll spend that on a shop diagnosis alone. If replacing these 3 items doesnt fix it then likely a vacuum line leak or tank pressure sensor (higher repair difficulty).

Also, make sure that the vent for the fuel tank is working. the vent is either on the fuel cap itself or thru a device commonly known as a duck bill valve, so named because of the shape of the valve. All the vent does is allow a slight amount of air to enter the tank while the trimmer is running.

P0440 - Evaporative Emission Control System Malfunction
Possible causes- Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking Tech notes Loose fuel tank filler cap is the most common cause that triggers the P0440 code.

a small amount of fuel leakege shouldnt hurt anything most gas tank vents are in the fuel cap if so replace cap

EVAP System Vent Circuit Malfunction

This diagnosis detects leaks in the Evaporative Emission (EVAP) purge line using of vapor pressure in the fuel tank. The EVAP canister vent control valve is closed to shut the EVAP purge line. The vacuum cut valve bypass valve will then be opened to clear the line between the fuel tank and the EVAP canister purge volume control solenoid valve. The EVAP control system pressure sensor can now monitor the pressure inside the fuel tank. If pressure increases, the Engine Control Module (ECM) will check for leaks in the line between the vacuum cut valve and EVAP canister purge volume control solenoid valve.

Possible causes
- Incorrect fuel tank vacuum relief valve
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- Leak is in line between intake manifold and EVAP canister purge volume control solenoid valve
- Foreign matter caught in EVAP canister vent control valve
- EVAP canister or fuel tank leaks
- EVAP purge line (pipe and rubber tube) leaks
- EVAP purge line rubber tube bent
- Blocked or bent rubber tube to EVAP control system pressure sensor
- Loose or disconnected rubber tube
- EVAP canister vent control valve and the circuit
- O-ring of EVAP canister vent control valve is missing or damaged
- EVAP canister is saturated with water
- EVAP control system pressure sensor
- Absolute pressure sensor

Possible solution
- Loose fuel filler cap
- Leaking fuel filler cap


Hope helps (remember to rate this answer).

This saw has a fuel tank vent that could be leaking a small amount of fuel, or the fuel line coming out of the tank could be leaking. Fuel line replacement isn't complicated, you could try installing a new one. If it's the vent, odds are it's not enough to cause alarm........unless the vent line is cracked. In that event, you should replace the vent hose. Again, not a complicated repair.

thier is also vent lines and return lines . be carful. see if it leaks whe its runing. or when you fill . if when runing could be return or pres . if when filling could be vent or fill hose .

Mitsubishi 2006 faulty fuel cap, leaking vent or purge solenoid, EVAP hose faulty or leak on fuel tank.... replace the fuel cap and a week later the light was back on...the code is P0442..what to do next

This saw has a fuel tank vent that could be leaking a small amount of fuel, or the fuel line coming out of the tank could be leaking. Fuel line replacement isn't complicated, you could try installing a new one. If it's the vent, odds are it's not enough to cause alarm........unless the vent line is cracked. In that event, you should replace the vent hose. Again, not a complicated repair.

This part is a vent solenoid to the EVAP system. The solenoid is controlled by the PCM & vents fuel vapors to the charcoal canister. If fuel is leaking here you should first make sure your vent in the gas cap is not clogged.This could cause a vacuum in tank & possibly lead to your problem, or the solenoid may have been damaged when the tank was removed & replaced.