The P0440 code is the result of a leak detected by the Engine Control Module (ECM), or a vapour pressure sensor has malfunctioned. The ECM monitors EVAP system pressure, and if it doesn’t maintain pressure, it will trigger the Check Engine Light.
The evaporative emission control (EVAP) system prevents fuel vapours from escaping into the atmosphere. When the vent control valve opens, the fuel vapours from the fuel tank travel through a vent line to the charcoal canister. The fuel vapours are then absorbed and stored by activated charcoal pellets in the charcoal canister. On the charcoal canister is a purge valve. When the purge valve is opened, the vacuum from the engine draws the fuel vapours out of the charcoal and into the engine intake manifold where it is then used as part of the air-fuel mixture needed for combustion within the cylinders of the engine.
When code P0440 is set, a leak has been detected by the Engine Control Module (ECM), or a vapour pressure sensor has malfunctioned. The ECM determines this when the vehicle is turned off, and the vent control valve is commanded closed. At this point, the ECM monitors EVAP system pressure, and if it doesn’t maintain pressure, it will trigger the Check Engine Light.
P0440 Code Symptoms
Check engine light
Fuel vapour odour
P0440 Causes are
Missing, defective, damaged, or loose gas cap (*Most Common)
Leaking or disconnected EVAP hose
Faulty purge volume valve
Faulty canister vent control valve
Charcoal canister leak
Leaking fuel tank
P0440 - DYI Steps to fix it
STEP 1: CHECK THE GAS CAP.
Inspect your gas cap to see if it is loose or damaged. If your gas cap is loose, tighten it. Inspect your gas cap for physical damage or deterioration. However, it should be noted that damage to the gas cap or deterioration of its components is not always visible. If your gas cap was not loose and you do not see any indications of failure, try replacing the gas cap anyway and clearing the codes. Gas caps are relatively inexpensive and are often the fix for code P0440.
STEP 2: RUN A SMOKE TEST.
If replacing the fuel cap didn’t fix it, perform an EVAP system leak check. Pinch off the vent tube to the EVAP Vent Control Valve. Pressurise the EVAP system with an EVAP smoke machine leak checker. Check to see if you see any smoke leaking out from any hoses or seals. Repair any leaks, clear the check engine light, and check to see if the problem is resolved.
STEP 3: CHECK PURGE VOLUME CONTROL VALVE.
If the code returns, test the Purge Volume Control Valve for a Stuck Open condition. With the key and engine off, remove the hose going to the Purge Volume Control Valve coming from the fuel tank and unplug the electrical connector to the valve. Performing this test may set another code. If it does, clear the code and disregard it until after the test is completed and the vehicle is put back together.
The EVAP purge volume control valve is usually located on or near the intake manifold. Start the engine and use either a vacuum gauge or your finger to see if the vacuum is coming out of the Purge Volume Control Valve where you removed the hose. If there is a vacuum, then the Purge Volume Control Valve is leaking and needs to be replaced. If there is no vacuum, you could still have an intermittent failure of the Purge Volume Control Valve or another EVAP system issue. Continue the diagnosis in the next step.
STEP 4: CHECK EVAP VENT CONTROL VALVE.
If the purge valve passes the test, check the EVAP vent control valve for proper operation. This valve can get sticky, have debris caught in it, or the internal solenoid can fail and not operate.
Remove the EVAP vent control valve from the vehicle. This is usually located under the car in the rear of the vehicle by or attached to the charcoal canister. Verify with no power or ground supplied that you can blow through the valve’s openings. If you can’t blow through the openings, the valve is stuck closed and needs to be replaced.
Supply power and ground to the solenoid. (Refer to your service manual for your vehicle to find out which pins to supply power and ground to.) The valve should click, and now you shouldn’t be able to blow through the openings. If you can blow through the valve when it is powered on, then the valve is faulty and needs to be replaced.
If the code returns, you will need further diagnostics by a mechanic. More diagnostic steps could require electrical testing of the purge and vent control valves for proper operation.
STEP 5: STILL NEED HELP FIXING P0440 CODE? CONSULT US.
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