P0440 Evaporative Emission Control System Malfunction | Car Troubleshooting

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P0440 Evaporative Emission Control System Malfunction



The P0440 code means that the control module has detected a leak in the evaporative emission (EVAP). Loose fuel tank filler cap is the most common cause that triggers the P0440 code. 

Malfunction is detected when the EVAP control system has a leak, the EVAP control system does not operate properly. 

 The Engine Control Module (ECM) tests the Evaporative Emission (EVAP) system for the following conditions: 

1. Large and small leaks. 
2. Excess Vacuum 
3. Purge Flow during non-commanded conditions. 
4. Fuel Level and Fuel Pressure Sensor faults. 
5. EVAP Purge and Vent Valve faults.

The ECM monitors the Fuel Tank Pressure sensor in order to determine the level of vacuum/pressure in the EVAP system. The ECM commands both the EVAP Purge Solenoid and the EVAP Vent Valve ON when the conditions are met in order to apply an engine vacuum to the EVAP system. The ECM commands the EVAP Purge Solenoid OFF once the system has reached a predetermined level of vacuum. This test verifies if a vacuum can be achieved in the EVAP system. Failure to develop a vacuum may be caused by a large leak or restriction.

Car Trouble Symptoms: 
1. The Check Engine Warning Lights will be “ON” 
2. Noticeable fuel odor caused by the release of fuel vapors.

Possible Cause of Problem: 
1. Fuel tank leaking. 
2. Missing or loose fuel cap. 
3. EVAP system hose leaking 
4. The use of an incorrect fuel filler cap. 
5. EVAP canister or fuel tank leaks. 
6. Fuel filler cap remains open or fails to close. 
7. Foreign matter caught in fuel filler cap.

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